Expected Threat (xT) for corners and free kicks

wa_setpieces.XTModel implements Karun Singh’s grid-based xT method: fit a grid of zone values from data, then value any pass as xT[end_zone] - xT[start_zone].

Important

The grid below is fit on a single match, purely to demonstrate the mechanism – it is far too little data for a trustworthy grid. Fit on a full season (concatenate many matches’ events) for real analysis, then reuse it with to_csv() / from_csv().

from pathlib import Path

from wa_setpieces import load_matches
from wa_setpieces.viz.plots import plot_xt_grid
from wa_setpieces.core.xt import XTModel, set_piece_delivery_xt, set_piece_xt_summary

try:
    _here = Path(__file__).resolve().parent
except NameError:
    _here = Path.cwd()
DATA = _here.parent / "tests" / "data" / "sample_match.json"

events = load_matches(DATA)

Fit the grid and look at it directly – value should climb steadily towards the opponent’s goal (x=100 in each event’s own attacking frame).

model = XTModel.fit(events, x_bins=8, y_bins=6)
fig, ax = plot_xt_grid(model)

xT added by every corner delivery (NaN where the corner didn’t find a teammate – there’s no reliable end location to value):

set_piece_delivery_xt(events, "corner", model)[
    ["eventId", "contestantId", "outcome", "xt_start", "xt_end", "xt_added"]
]

	eventId	contestantId	outcome	xt_start	xt_end	xt_added
0	191	f2yd0yzt0om6qhks9gbowu1d6	0	0.008352	0.250000	NaN
1	223	cxb4hqite921i36gwrezdts7c	1	0.023828	0.004661	-0.019166
2	404	cxb4hqite921i36gwrezdts7c	0	0.023828	0.250000	NaN
3	482	f2yd0yzt0om6qhks9gbowu1d6	0	0.008352	0.254417	NaN
4	610	f2yd0yzt0om6qhks9gbowu1d6	0	0.023828	0.254417	NaN
5	613	f2yd0yzt0om6qhks9gbowu1d6	0	0.023828	0.254417	NaN
6	723	f2yd0yzt0om6qhks9gbowu1d6	1	0.023828	0.023828	0.000000
7	730	f2yd0yzt0om6qhks9gbowu1d6	0	0.008352	0.250000	NaN
8	786	f2yd0yzt0om6qhks9gbowu1d6	0	0.023828	0.250000	NaN

Rolled up per team, for both corners and free kicks:

set_piece_xt_summary(events, "corner", model)

	contestantId	deliveries	successful_deliveries	total_xt_added	avg_xt_added
0	cxb4hqite921i36gwrezdts7c	2	1	-0.019166	-0.019166
1	f2yd0yzt0om6qhks9gbowu1d6	7	1	0.000000	0.000000

set_piece_xt_summary(events, "free_kick", model)

	contestantId	deliveries	successful_deliveries	total_xt_added	avg_xt_added
0	cxb4hqite921i36gwrezdts7c	12	9	0.000515	0.000057
1	f2yd0yzt0om6qhks9gbowu1d6	13	9	0.005945	0.000661