Portuguese prosecutors are investigating the conduct of a policeman who beat a man in front of his young children and also punched their grandfather outside a soccer stadium, sparking a national scandal.

Police approached Jose Magalhaes outside the Guimaraes stadium where Benfica had just won the Portuguese league title on Sunday. Magalhaes said police had allowed him and his two sons, who were wearing Benfica jerseys, to leave the stadium before other fans because the children were being crushed.

Footage shows an officer questioning Magalhaes, then punching his elderly father before using a truncheon to beat Magalhaes, who was on the ground, while his 9-year-old child screams "Dad! Dad!"

The district prosecutor said in a statement late Tuesday that it has opened an investigation into alleged abuse of power.