Evaluating goal threat in football using player and ball locations

Goal scoring in football is relatively low but vitally important, hence research has considered how goals are created and scored with measures such as expected goals prevalent. The dynamical systems theoretical perspective, considers a collective system, such as football, as existing in two states, stable (no substantive advantage for either team) or unstable (advantage present). Hence, goal scoring events occur when the system has become unstable, with a “perturbation” the event causing the system state change. Here, a “goal threat” value was calculated every second (scaled from 0 to 100) using the XY coordinates of players and the ball, weighted in relation to proximity to the goal (a potential proxy for the degree of system instability). Video recordings and synchronised Amisco 2D representations of goals (n=64) scored in Swansea City AFC English Premier League 2012/2013 matches (n=20) were analysed using Dartfish v10 Pro software. Each goal was analysed from when the play was judged to be stable (no obvious goal scoring opportunity), or the start of possession, until the goal had been scored. Goals were not always preceded by high goal threat values (maximum goal threat values ranged from 13.4 to 99.0). The authors independently subjectively determined that perturbations occurred up to 7 seconds from when the goal threat value increased by at least 40%. Thus, perturbations were not directly related to goal scoring opportunities. This novel method provides a useful, quantifiable, and simple measure of goal threat that may also aid audience engagement and measure defensive effectiveness.

Zadetki v nogometu so ključnega pomena. Ker je le teh relativno malo, smo preučevali, kako se gol doseže. V ta namen smo uporabili koncept prevladovanja pričakovanih golov. Teoretična perspektiva dinamičnih sistemov je preučila nogomet kot kolektivni sistem, ki obstaja v dveh stanjih - stabilnem (brez prednosti za nobeno ekipo) ali nestabilnem (s prednostjo eni ekipi). Pri doseganju golov se sistemi spremenijo iz stabilnega v nestabilno stanje, pri čemer se \"motnja\" pojavi kot dogodek, ki povzroči spremembo stanja sistema. V raziskavi je bila izračunana vrednost \"grožnje golu\" za vsako sekundo, ki je upoštevala položaj igralcev in žoge ter oddaljenost od gola (kot približek za stopnjo nestabilnosti sistema). Za analizo je bilo uporabljenih 64 golov, doseženih na tekmah angleške Premier lige Swansea City AFC v sezoni 2012/2013, ki so bili predstavljeni v videoposnetkih in 2D animacijah programa Amisco. Vsak gol je bil analiziran od trenutka, ko je bila igra ocenjena kot stabilna, ali od trenutka, ko je ekipa pridobila posest žoge, do trenutka, ko je bil gol dosežen. Pred golom vrednosti grožnje niso bile vedno visoke, najvišje vrednosti so bile med 13,4 in 99,0. Ugotovili smo, da se je motnja običajno pojavila v roku 7 sekund od trenutka, ko se je vrednost grožnje povečala za vsaj 40% in da motnje niso nujno povezane s priložnostmi za gol. Ta nova metoda zagotavlja uporabno in merljivo merilo grožnje golu, kar lahko pomaga tudi pri angažiranju gledalcev in merjenju učinkovitosti obrambe.