Major League Soccer announced on Thursday that a fourth substitute will be available to teams during 2017 MLS Cup Playoff matches that require extra time.
The International Football Association Board (IFAB), which oversees changes to the Laws of the Game, has approved experiments for a fourth substitute in extra time. Under the IFAB regulations, a fourth substitute may only be used if a game goes to extra time and may be used regardless of the number of substitutes a team made during normal time. Fourth substitute experiments have already been run in the FA Cup, Scottish Cup, FIFA Confederations Cup and FIFA Club World Cup – a final decision on the incorporation of a fourth sub will be made by IFAB in 2018 or 2019.