Is it haram to play a video game or watch a sports match when flags of non-Muslim countries appear that contain haram (like a cross)? eg, a soldier in a video game might be wearing the UK flag on his shoulder, or a tv match might show nothing objectionable except a team's flag containing a cross

Ustadh AbdulAziz al-Haqqan

Not necessarily, as this is a coincidence and it goes away quickly.