The ferocious Islamic death cult had banned organised sports like football when they took over Raqqa in Syria more than two years ago.
The victims, who were executed in front of a crowd of children in Raqqa, were also accused of spying for the Kurdish YPG rebels.
A fifth unknown man was also killed.
Gruesome pictures of the execution – which shows children inspecting the bodies of the victims – were posted on a dissident group’s Twitter feed.
In a series of tweets, Raqqa is Being Slaughtered Silently named the victims as Osama Abu Kuwait, Ihsan Al Shuwaikh, Nehad Al Hussen and Ahmed Ahawakh.
They shared pictures of the men in their Al-Shabab kits.
It is not the first time ISIS has targeted the sport of football.
Last year, militants executed 13 teenage boys for watching the Asian Cup football match between Iraq and Jordan.
The young football fans had been caught watching the game on television in the Iraqi city of Mosul, which is controlled by the Islamic State.