Effect of game state and opposition on Expt Pts

July 5, 2018

Despite creating an Expt Pts model (outputs are here for anyone interested) I am acutely aware of its limitations. There are so many factors that can go into whether a shot is successful or not that only taking three elements (shot type, shot location and whether it is a goal attempt or not) seems arbitrary. It leaves the metric incomplete.

Now don’t get me wrong. I still believe that Expt Pts is a better metric than Conversion Rates (which are better again that just counting wides!) but at the moment it is a tool that allows you to quickly hone in on particular areas of the game rather than being an absolute barometer.

So the question arises. How do we make it better?

The first port of call is to look at what other sports are doing. Both Soccer (through Xg) and the NFL (through DVOA) place emphasis on the game state and the quality of opposition.

We are limited in the GAA by the availability of raw data but at Christmas I was able to post the below graph on Twitter (@dontfoul) which shows that there is definitely a game state effect. (People were generous enough not to point out my spelling of “deficit” – D’oh!)

Was there also a “strength of opposition” effect as well? And if so can we combine the two to create a more refined Expt Pts?

Strength of Opposition
The games used in this review are 2015 – 2017 Championship games. In that timeframe we want to somehow grade/tier all the teams to see if playing up, or down, to your level has an effect on Conversion Rates.

So how do you Grade a team (see Note1)? My approach was a mixture of subjective and objective. From ’15 to ‘17 three teams – Dublin, Kerry and Mayo – were ahead of the rest occupying 9 of the 12 semi-final berths. Go back to 2014 and it is 12 of the 16 semi-final berths with the only non-Big three to make the final in those four years being Donegal. They are our (subjective) Tier1.

It is possible to make a whole army of mini tiers all the way down the 32 counties thereafter but we will then run into sample size issues for any output. Plus it is very rare for those teams in Division4 to compete in TV games, which is essentially what we have to work with, so we do not need a whole host of Tiers. Instead we just need big enough ones that are appropriate.

So I came up with a rules based approach to split the remaining 28 counties (excluding New York & Kilkenny) more or less in two.

All teams in that years’ Division1, outside the Big 3, plus all teams in Division2 are Tier2 as is any team from Division3 and 4 that made the Championship QF. This gives us an objective grading system with the ability to upgrade teams that played well but also stable enough year on year.

It is not perfect. It has an element of subjectivity. But it does the job required.

So we have our teams graded according to their overall relative strength. Does it work? Is there an effect? Intuitively it should. It just makes sense that Dublin will convert more against Antrim than they would against Tyrone. Or that conversely Laois would struggle when playing up a level against Dublin but less so when playing Wexford.

Also we have seen this effect in action previously when we calculated Conversion Rates after overlaying the pressure applied to shots (implication being that “better” teams will apply more pressure to shots and vice versa).

Finally we also have an inbuilt test. If the Grade shows itself up in open play it really shouldn’t from frees. Why would taking a free against Tyrone be any different than trying the exact same free against Offaly? So the expectation is that when we break teams’ Conversion Rates down by Grade attempts from play will vary but those from frees won’t.

And that is exactly what happens.

Irrespective of the opponent Conversion Rates on frees (only frees taken inside the 45 were included to remove as many outliers as possible) are very stable. The volumes are decent as well with just over 1,000 frees included.

The big eye opener however is what happens to attempts from play. As you go up the Grades/Tiers there is steady fall off in Conversion Rates. If, for example, Meath play Dublin then the Conversion Rate is 38.7%. Against Kildare it increases to 45.6% and against Wicklow it jumps again to 51.2%. The same phenomenon can be seen in goal attempts. The “better” the opposition the lower the Conversion Rates.

This all makes sense but the implications for Expt Pts, and anyone looking to use any version thereof, are quite big. Expt Pts currently run off averages … those averages are taken as a whole from all games. They need to be calibrated for opponent.

Game State
So now that we have strength of opposition what about game state? The original chart above showed that there was an affect but that was too simplistic. Registering all scoreboard differences as the same is not right (taking a shot two points down in the first half is not quite the same as having an attempt two points down in the 60th minute). We have to further refine the criteria.

Right now we don’t need to define what the optimum criterion is. We are just trying to show/prove if there is indeed an affect. To that end I have extracted all shots taken under a “clutch” situation – defined as any shot in the 2nd half of a game where there is only three points in it – and compared them to “non-clutch” shots.

Again we could define it differently – say only include games within two points from 60th minute onward – but this will give us volume issues.

So what are we expecting to see? Conversion Rates to be lower across the board in clutch situations. The real test however is that that frees should, unlike when looking at Grading above, be affected by this new scenario. If there is “scoreboard” pressure it should affect frees as well as point attempts.

And once again there is an affect. The Conversion Rates for both frees and point attempts from play disimprove in tighter game scenarios. Again all very sensible.
Finally overlaying the two we can see that the greatest discrepancies happen in, subjectively, the scenarios people are most unaccustomed to.

Lower level teams, with a shot of winning the game in the 2nd half against higher quality opponents, convert only ~31% of their point attempts as against ~40% for the rest of the game. The “deer in the headlights” syndrome.

There is also a minor drop off when teams are playing against opponents of similar, or lower, ability but it is nowhere near as stark.

So there we have it Scoreboard pressure is indeed a thing. The opponent grade matters. And whilst very useful the simplistic Expt Pts model is nowhere near complete.

Appendix
Note1; We could look at grading teams via their defensive performance in that period but some teams rarely, if ever, compete in TV games. How do you grade a defence based on performance metrics if you’ve never seen them?

Note2;

2017 Grade2 teams
Division1 that year; Tyrone, Donegal, Monaghan, Cavan, Roscommon
Division2 that year; Cork, Derry, Kildare, Meath, Down, Galway, Fermanagh, Clare
Division 3 or 4 that made it to the QF; Armagh

Grade 3 – Westmeath, Laois, Louth, Wexford, Limerick, Longford, Sligo, Offaly, Tipperary, Wicklow, Leitrim, Waterford, Antrim, London, Carlow, London

Advertisements

Dublin v Donegal 2016 League SF

April 12, 2016

There is no point pretending that this game was anything other than a run out. As Chris McNulty commented on Twitter (@chrismcnulty86 – a good follow on all things Donegal) Donegal took the game so seriously that they didn’t train all week. I have completely forgotten who, so apologies for not crediting, but some other wag commented that it was like an exhibition match at the opening of a new ground (see note1). It just had that feel to it.

Still. The two teams may not have engaged as if it were the height of Summer but we we’ll fire up the numbers and see what it throws up.

Team Possessions Attacks Shots Scores Exp Pts
Dublin 52 46 30 1 – 20 18.87
Donegal 46 38 27 0 – 13 16.08

In the opening league game between these two Dublin were restricted to a 76% attack rate and 21 shots. Here it was an 88% attack rate and 30 shots. Again in that opening game Dublin managed (or maybe more accurately the Donegal defense allowed) 0.29 points per possession. Here it was 0.44. There was just no bite to Donegal.

It was not like there was a huge difference in opportunities between the halves either. The goal at the start of the second half did not see Donegal switch off. Both, by some statistical quirk, had stat lines of 26 possessions with 23 attacks and 15 shots. Dublin were slightly more accurate in the first half with a conversion rate of 73% (0-11 from the 15 shots) though the second half conversion rate of 67% (1 – 09 from 15) was also very efficient.

Although they may not take much from the game one positive aspect, from a Dublin perspective, is that their early accuracy came despite the fact that two of their main strife force, Brogan & Mannion, combined for a mere two shots in the first half.

What of Donegal? It may come as some surprise to note that – in pure shooting terms – they were not all that far behind Dublin.

Dub - Don league SF Expt Pts

The above graph shows the team’s respective shooting broken down into actual score vs Expected score (see note2). Donegal, despite what was noted above re application, were on track with Dublin up until the ~33rd minute. Dublin tagged on 0 – 03 at the end of the first half and kicked off with a goal at the start of the 2nd but up until then Donegal were right with them.

The “but” quite obviously comes with caveats. The first being that whilst teams with average returns from the shots attempted would have been level around the 33rd minute Dublin are not average. Nor in their own ways are Mayo or Kerry. Dublin outperformed their Expt Pts from the get go (as an aside Kerry did something vaguely similar against Cork. That day they score 0 – 10 from their first 12 shots inside 20 minutes and were up and gone. It will be interesting to see the starts both teams make, or are allowed make, in the final. But I digress). On top of this Donegal lagged behind what was expected. One of the hallmarks of the 2012 & 2014 teams was their remarkable accuracy in games where the shot counts were very low. They will need to regain this accuracy.

A second point on the Donegal shooting was just how reliant they were on Murphy & McBrearty. Here they accounted for 70% of Donegal’s shots (Dublin’s top 3 marksmen in terms of Volume – Rock, Brogan & Kilkenny accounted for 52% combined). In the opening league game this duo accounted for a more realistic 45% of shots.

Part of this over reliance on Murphy & McBrearty was Donegal’s volume of shots from frees. In total they had 11 shots on goal from free kicks. Dublin had a mere four (plus one 45). Relying on frees as a way to keep the scoreboard ticking over is a tried and trusted manner but in many ways it is dicey proposition as gaining a free is not always within your control. You are reliant on the defender’s, and perhaps more importantly the referee’s, complicity.

Finally Dublin’s Expt Pts was boosted by creating goal chances. They had four shots at goal in total scoring 1 – 01 (about what is expected). Donegal only manufactured the one shot at goal and that a weak, in terms of where the shot was taken from, one from Murphy in the dying embers of the game that went straight at Cluxton. In fairness in the three other Donegal league games that I charted (Roscommon, Kerry & Dublin) they came out even in goal shots in all three so this game may not be emblematic.

So is there hope for Donegal? Absolutely. Over the two games they created as many shots as Dublin. In the first game, when they were not at full tilt but were at least more inclined to try than here, they were able to restrict Dublin’s shooting. But there are also some obvious dangers. They must ensure the shooting volumes are not as concentrated as in this game and also improve their accuracy from play (1-06 from 27 shots over the two Dublin games for a success rate of 26%). The control – in terms of game tempo and shot selection – needs to re-emerge. Goals need to be kept to a minimum. The restrictive game plan does not lend itself to chasing games.

Note1; if you have a twitter account it’s probably better to follow me there (@dontfoul). I tend to have game “scorecards”, like the below, up a lot quicker than the blog posts. Plus by having the game capsule up there I don’t feel the need to get every stat up here!

Dub%20-%20Don%20league%20SF%20Overview

Note2; I have a piece half written on Expected Points which I will publish prior to the Championship. In essence it is the same measurement as the weighting that has been used heretofore but (hopefully) is a lot more readily understood.

Appendix

Shot Charts

Dublin’s shooting
Dublin shooting (V Donegal 16 league SF)

Donegal’s shooting
Donegal shooting (V Dublin 16 league SF)
x = missed, disc = score, yellow = deadball, black = normal time from play, red = goal attempt

An Ode to Cillian O’Connor’s right foot

October 28, 2014

Originally this was going to be a follow up to the deadball accuracy piece in which I would highlight any interesting tidbits that had popped up whilst reviewing the past three years. Instead it is going to be an ode to Cillian O’Connor.

Attached below is the chart I initially posted on twitter (@dontfoul) showing the accuracy for the players with the ten most attempts since 2012.

 

Player deadball

 

O’Connor came out on top in terms of Success Rate. But he did so whilst also attempting the most deadballs. He had volume on top of his accuracy. He also maintained this accuracy in some of the most highly pressurised situations. In the three year span that the returns covered Mayo have appeared in 13 TV games with three quarter finals, four semi finals and two finals amongst them. Most impressive.

 

Deadball accuracy v2

 

What is even more impressive is the fact that O’Connor has recorded the highest weighting in this interval as well. He is not just tapping over simple 14m frees to maintain his Success Rate. His weighting reflects the fact that he is converting frees of an above average difficulty at an above average frequency (as a counter point note Bernard Brogan – a well above average Success Rate but a barely positive weighting – he is merely converting the frees that an average free taker would convert but because of Dublin’s volume of attacks he gets to take more frees).

It is not just volume that is leading to a higher weighting either. On current trajectories only Cluxton is in line with his weighting. So how has he done it?

 

Deadball Type Attempts Scores Success Rate Average Weighting
Frees
inside 20m 24 23 96% 88% +2.64
20m to 45m 35 30 86% 71% +5.375
outside 45m 3 0 0% 40% -1.210
total 62 53 85% 72% +6.803
45s 7 4 57% 47% +0.630
Penalties 3 3 100% 82% +1.778

 

O’Connor’s accuracy is above the average in all three of the deadball categories – frees, penalties & 45s – that he has attempted. His weighting has been aided by converting three penalties (for a longer explanation on why penalties have such high weighting see here) but on the flip side he has attempted three frees from outside the 45 for which he patently does not have the “legs”. As an illustration see a chart of all his deadballs, excluding penalties, this year.

 

OConnor14
x = missed, disc = score,black = free, white = 45

 

O’Connor’s only missed two frees from inside 40 metres in 2014 and one of those was the desperation goal attempt in the semi final replay at the end of extra time. His accuracy from c40 metres in is genuinely exceptional.