So why did Donegal keeper Shaun Patton have to return to the pitch from the halfway line after being treated for injury in their Ulster SFC quarter-final win over Derry?
The Donegal stopper went down with a leg injury around the 23rd minute of the game and was soon requested to leave the field of play by referee David Gough.
When Patton then looked to re-enter the play from behind his goal, he was instructed - by referee Gough and by his team-mate Ryan McHugh - to make his way to the halfway line where he would be permitted to return to the action once there was a break in play.
This led to a brief passage of play where Donegal were down to 14 men and had no goalkeeper on the pitch as they defended a throw-in on their own 21-yard line.
The injury would eventually force Patton off the pitch for good, in the 55th minute. Back-up keeper Gavin Mulreany replaced Patton for the final 20 minutes of playing time.
A new rule in place this season means a player not seriously injured who requires treatment must be treated off the pitch and can only return at the halfway line during a break in play - and with the referee's permission.
A player being treated for a serious injury is permitted to remain on the field of play.
Watch Mayo v Roscommon in the Connacht Football Championship semi-finals on Sunday from 3.40pm on RTÉ2 and RTÉ Player, follow a live blog on rte.ie/sport and the RTÉ News app and listen to updates on Sunday Sport on RTÉ Radio 1
