Table 1.  Possible associated factors.

Associated factor

Sydney Roosters series

FC Barcelona series

Chance

A factor, but unlikely to fully explain the cluster

A factor, but unlikely to fully explain the cluster

Past injury history of players

Not a relevant factor

A factor for 2/4 players

Player boot selection

Not apparently relevant as different boots used, although 3/4 players used blade configuration boots.

Not apparently relevant as different boots used

Specific preventive training

Players had only done their usual training program

Players had undertaken a specific program designed to prevent ACL injuries

Ground of injuries

Away

Home

Time of injury (in game)

2/4 were early in the first half

3/4 were early in the first half

Timing of injuries (in season)

Mid-season

3/4 were early in the season after players had undergone limited pre-season preparation

Playing surface

Newly laid bermudagrass squares, of apparently poor quality installation (uneven, heavily sand topdressed)

Newly laid Kentucky bluegrass/ryegrass squares of apparently good quality; traction 48 Nm.