Your sports team requires you to be on this group chat, but sends videos of naked women in the same chat? What kind of team is this? School? Recreational?
I'll divide my response into cases.
Case 1: This is a casual sports team and you guys are just friends who kick a ball around. Tell them you don't like it. Tell them it's inappropriate in a respectful and courteous way. If they don't accept your feedback, leave and never talk to them again, they are a horrible influence to you and others. You'll just have to deal with finding another group.
Case 2: This is a professional sports team. Do the same as in Case 1 <OR > report them to the coach/supervisor. Carry on from there.
Case 3: This is a school/college team. Do the same as in Case 1 <OR > Report them to the superintendent/dean for sexting and have them expelled.