Contribution to risk assessment in football by video analysis of overstepping boundary line events

The aim of this paper was to investigate prerequisites for safety equipment in the surrounding area of soccer playing-fields. Therefore, the frequency and location of overstepping boundary line events (OBEs) occurring when football players are crossing the boundary lines and leaving the regular field. Commercial television video footage of 28 matches in UEFA European Championship 2012 and of 46 matches in FIFA World Cup 2006 were analysed. To accurately identify portions of playfield outline where an OBE occurred, the four different field lines, two Goal lines and two Side lines were divided in 46 segments, defined as “boundary-line-segment” (BLS). Statistical analysis was used to prove if OBEs were uniformly distributed over all playfield BLSs. The results indicated remarkable differences in OBE frequencies among football field areas. In particular, goal-line-BLSs have shown to be the most critical zones of the pitch outline, with different number of OBEs on the two goal lines. This opposes the expected symmetry in OBE distribution as a consequence of the usually adopted directions of football playing and equal boundary areas surrounding goal posts. Furthermore, absolute OBE frequencies on Side line near to the technical area appeared to be greater than the homologues on the opposite side line. The distribution pattern of OBEs over all BLS can be explained by two main influencing effects: the side line effect (SLE—players behave differently at the sideline of the technical area compared to opposite side line because of different distance to advertisements boards) and the leg side effect (LSE—most players prefer to use their right leg to kick the ball). Findings in terms of OBE frequencies should be taken into account to establish right priority of actions for safety intervention by responsible and technicians of Sports fields.