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Toolkit
Tools, datasets, and model references for exploring set-shot decisions.
AFL Set Shot Guide
A brief guide to set shots, expected value, and reading the model.
An AFL set shot is a kick at goal taken after a mark or free kick. The player has time to set up, so distance and angle become major parts of the decision. A central 45-metre shot can be very different from a wide 45-metre shot, even if both are recorded as the same distance from goal.
Expected value estimates the average points a choice is worth over many similar possessions. A shot worth 2.4 expected points is not predicted to score exactly 2.4 points once. It means across similar possessions, every time you take the shot, on average you will earn 2.4 points per possession. So across similar 100 possessions, you'd expect to earn 240 points from taking the shot
Long set shots are often passed off because a teammate may get a closer kick. The pass has to be marked first, though. If the mark is unlikely, the original kicker may only need to be a modest goal chance for taking the shot to be the better possession.
Pass mark rate is the chance the ball is successfully marked by the teammate at the second-shot location. For example, a 25% pass mark rate means 25 of 100 pass attempts are marked before the teammate can take the next set shot.
Behind rates matter because a missed goal can still score one point. A low-accuracy long shot can still have useful expected value if many of the misses score behinds, while a failed pass may produce no immediate score.
The recommended play is the higher expected-value option under the current map locations and model controls. If the set-shot EV is higher, the model favours taking the shot. If the pass option EV is higher, it favours passing.
Model Formulas
Formulas for comparing set-shot EV, pass EV, mark rate, behinds, optional unmarked-pass scoring, and play-on scoring.
EV = Accuracy x 6 + (1 - Accuracy) x 1
The basic expected value of a set shot. A goal is worth 6 points. This simple version assumes every missed goal still scores a behind worth 1 point.
EV = Accuracy x 6 + (1 - Accuracy) x behindRate
The adjusted version used by the sliders. The behind rate is applied only to shots that miss the goal. For example, a 50% accurate shot with a 65% behind rate gives 50 goals plus about 33 behinds from the 50 missed goals.
EVO = accO x 6 + (1 - accO) x behindRateO
The expected value of taking the original shot from where the mark or free kick was paid: goals first, then behinds from the share of missed goals that still score.
EVX = accX x 6 + (1 - accX) x behindRateX
The value of the shot after a successful pass is marked: goals first, then behinds from the share of missed goals that still score. This is calculated before applying the chance that the pass is actually marked.
passToMarkRate = 1 - playOnRate
This is the share of pass-option possessions that still become pass-to-mark contests after the play-on branch is applied. If the Play-On Rate toggle is off, playOnRate is 0 and passToMarkRate is 1.
MarkContestEV = (markRate x EVX) + ((1 - markRate) x unmarkedShotRate x unmarkedAverageScore)
This is the value of the pass-to-mark branch before the play-on rate is applied. Successful marks use the X set-shot EV. Unmarked passes use unmarkedShotRate for how often a loose pass still generates a shot chain, then unmarkedAverageScore for that chain's expected points.
PlayOnEV = playOnAverageScore
This is the value of pass-option possessions that turn into play-on instead of pass-to-mark contests. If the Play-On Rate toggle is off, this branch contributes 0 to the pass option.
PassEV = passToMarkRate x MarkContestEV + playOnRate x PlayOnEV
The full pass option EV combines the pass-to-mark branch with the play-on branch. If the Play-On Rate toggle is off, passToMarkRate is 1 and the model reduces to the mark-contest branch.
PassEV = (1 - playOnRate) x [(markRate x EVX) + ((1 - markRate) x unmarkedShotRate x unmarkedAverageScore)] + playOnRate x playOnAverageScore
This is the pass option written out in full. The first term values the pass-to-mark contests using successful marks plus optional unmarked-pass scoring. The second term adds average points from play-on possessions when Play-On Rate is turned on.
ShotEdge = EVO - PassEV
Shot edge is the O set-shot EV minus the pass option EV. Positive means the shot is ahead. Negative means the pass is ahead.
UnmarkedEV = unmarkedShotRate x unmarkedAverageScore
This only applies after a pass-to-mark contest is not marked. In MarkContestEV, the marked branch is markRate x EVX, while the unmarked branch is (1 - markRate) x UnmarkedEV. If this toggle is off, UnmarkedEV contributes 0.
markRateNeeded = (EVO - playOnRate x playOnAverageScore - passToMarkRate x UnmarkedEV) / (passToMarkRate x (EVX - UnmarkedEV))
This is the break-even mark rate needed for passing to match shooting after accounting for the play-on branch and optional unmarked-pass scoring. If Play-On Rate and Unmarked Shot Rate are both off, this simplifies to EVO / EVX.
accO = (PassEV - behindRateO) / (6 - behindRateO)
The direct goal accuracy needed tells you how accurate the original shot must be for shooting to equal the current pass option under the active mark-rate, behind-rate, and pass-leading-to-score assumptions.
DecisionEV = OShotEV - PassEV
DecisionEV = [accO x 6 + (1 - accO) x behindRateO] - {(1 - playOnRate) x [markRate x [accX x 6 + (1 - accX) x behindRateX]+ (1 - markRate) x [unmarkedShotRate x unmarkedAverageScore]] + playOnRate x playOnAverageScore}This is the complete decision comparison. The O shot side includes the original goal accuracy and original behind rate. The pass side includes play-on scoring, pass-to-mark contests, the X shot goal accuracy and behind rate after the mark, plus optional average-score value from unmarked passes. A positive DecisionEV favours taking the shot; a negative DecisionEV favours passing.