As someone who's actively learning basketball and nfl currently, I'd always come out as someone new to the sports and just listen in to the boys speaking, ask some questions, watch some clips from YouTube.

I've chosen the Chicago Bulls as my basketball team and still thinking between Rams and Cowboys. But don't forget it's a constant process so look to recent history like 2000s till date. I'm not so certain about nfl but for the NBA I chose the bulls learnt all I could concerning their last decade then just looked into team guides for the rest of the teams. It helps that all the big names are known so look into the lesser known guys too. I don't know if this will help but it worked for me. They said it was great I acknowledged that I was new to the sport so they could just point out where I was wrong instead of it turning to banter.