Pittsburgh Steelers rising star Chase Claypool sent an autographed jersey to a 76-year-old fan after learning of the man's recent dementia diagnosis ... and it's emotional.
Claypool -- a rookie WR who's BALLED OUT in recent weeks -- saw a TikTok video that explained the fan's battle ... and Chase was clearly moved by the whole thing.
In the clip, the fan's son explained his dad is "the biggest Steeler fan in the world" ... but is now having trouble remembering players' names on a weekly basis.
So, Claypool decided to send him some BIG love .