Design/methods:Eighteen Belgian assistant referees were included in the experiment. Ten assistant
referees (i.e., training group) were exposed to a pre- and posttest and, in between, four off-field offside
training sessions via a web-based training protocol. The remaining eight assistant referees participated in
the control group and only completed the pre- and posttest. During both test sessions, which were
conducted separately for each group, both an on- and off-field offside decision-making test was
completed.