Background Hamstring muscle injury (HMI) is the most common injury in professional football and has a high re-injury rate. Despite this, there are no validated criteria to support return to play (RTP) decisions.

Aim To use the Delphi method to reach expert consensus on RTP criteria after HMI in professional football.

Methods All professional football clubs in England (n=92) were invited to participate in a 3-round Delphi study. Round 1 requested a list of criteria used for RTP decisions after HMI. Responses were independently collated by 2 researchers under univocal definitions of RTP criteria. In round 2 participants rated their agreement for each RTP criterion on a 1–5 Likert Scale. In round 3 participants re-rated the criteria that had reached consensus in round 2. Descriptive statistics and Kendall's coefficient of concordance enabled interpretation of consensus.

Results Participation rate was limited at 21.7% (n=20), while retention rate was high throughout the 3 rounds (90.0%, 85.0%, 90.0%). Round 1 identified 108 entries with varying definitions that were collated into a list of 14 RTP criteria. Rounds 2 and 3 identified 13 and 12 criteria reaching consensus, respectively. Five domains of RTP assessment were identified: functional performance, strength, flexibility, pain and player's confidence. The highest-rated criteria were in the functional performance domain, with particular importance given to sprint ability.

Conclusion This study defined a list of consensually agreed RTP criteria for HMI in professional football. Further work is now required to determine the validity of the identified criteria.