Operational definitions
| Training session | Team training that involved physical activity under the supervision of the coaching staff |
| Match | Competitive or friendly match against another team |
| Injury | Any physical complaint sustained by a player that resulted from a football match or football training and led to the player being unable to take full part in future football training or match play |
| Hamstring injury | An acute onset distraction injury or gradual onset injury to the hamstring muscle group |
| Recurrent injury | Injury of the same type and at the same site as an index injury occurring previously during the same season |
| Early recurrence | Recurrent injury that occurs within 2 months after return to full participation from the index injury |
| Injury incidence | No of injuries per 1000 player hours ((Σ injuries/Σ exposure hours)×1000) |
| Injury burden | No of lay-off days per 1000 player hours ((Σ lay-off days/Σ exposure hours)×1000) |