He vowed to give charity if the team he supports won the match

Praise be to Allah.

Shaykh ‘Abd ar-Rahmaan al-Barraak was asked this question and he replied: 

He is obliged to give charity, but this is blameworthy according to sharee‘ah for two reasons: 

1.He connected his vow to a kind of idle pursuit that is blameworthy according to sharee‘ah

2.It is a conditional vow, and conditional vows are haraam or makrooh; they do not put back anything that Allah has decreed; rather all they do is get something out of the miser.