i love playing sports with my gf

My girlfriend and I have been dating for sometime now and we have our ups and downs like most relationships. We have been trying to find something fun to do together and she mentioned that she has been playing in a flag football league yearly. Some of these people are friends others she meets new every year. Im an athletic guy and she had mentioned that she was trying to find more people to make the team complete and I said I would love to play and she instantly rejected the idea and says this is something she does on her own and doesnt like her significant other to do with her.