Table 1

Operational definitions used in the study

Training sessionTeam training that involved physical activity under the supervision of the coaching staff
MatchCompetitive or friendly match against another team
InjuryAny physical symptom sustained by a player as a result of a football match or football training that led to the player being unable to take full part in future football training or match play
Hamstring injuryA traumatic distraction or overuse injury to the hamstring muscle group (the musculotendinous complex of biceps femoris, semitendinosus and semimembranosus) including both first-time and recurrent lesions
RehabilitationA player was considered injured until team medical staff allowed full participation in training and availability for match selection
Lay-offNumber of days until the player resumed full team training
Early recurrenceInjury of the same type and at the same site as an index injury occurring within 2 months of returning to full participation after the index injury
Slight/minimal injuryInjury causing 0–3 days absence
Mild injuryInjury causing 4–7 days absence
Moderate injuryInjury causing 8–28 days absence
Severe injuryInjury causing >28 days absence
Traumatic injuryInjury with sudden onset and known cause
Overuse injuryInjury with insidious onset and no known trauma