1920s Fort Pitt football question

[L.C. Greenwood]

Hoping someone can help me with an historical football question this morning. I have a grandfather who played semipro football for Fort Pitt/Arlington from 1922-28, the uniforms had a "FP" on the front of the jersey. Unfortunately, I failed to get any substantial information about his playing experience while he was alive, don't even know what league or association was involved. I've struck out researching this issue online, so if anyone could point me in the right direction it would be appreciated.