Operational definitions
| Injury | Injury resulting from playing football and leading to a player being unable to fully participate in future training and match play (ie, time-loss injury) |
| Muscle injury | Indirect or direct injury to the muscle leading to a player being unable to fully participate in training or match play |
| Return to play | Full participation in training and availability for match selection |
| Indirect muscle injury | A muscle injury caused without the influence of a direct external trauma |
| Functional muscle injury | Painful muscle injury/disorder (acute or chronic) without macroscopic evidence of muscle fibre damage (seen in ultrasound/MRI) |
| Structural muscle injury | Any acute indirect muscle injury with macroscopic evidence of muscle fibre damage (seen in ultrasound/MRI) |
| Direct muscle injury | A traumatic muscle injury caused by a direct (blunt or sharp) external trauma |
| Contusion | Tissue bruise without concomitant injuries classified elsewhere |
| Muscle contusion | Direct muscle trauma, caused by blunt external force |
| Laceration | Direct trauma including skin and subcutaneous tissue, caused by sharp external force |
| Foul play | Violation of the laws of the game according to the match referee |
| Lay-off/absence | Number of days until the player resumed full team training |
| Re-injury/recurrency | Injury of the same type and at the same site as an index injury occurring no more than 2 months after a player's return to full participation from the index injury |