Eckstein isn't even that big now! Besides, the little Eck's a towhead. This guy never played for the MLB Cards.
There has to be a Red Sox connection or you wouldn't have posted it. I'll write off anybody before 1950, color snap shots weren't around commonly till the mid to late fifties. Yaz grew up in NE so I doubt he was a Card fan, I doubt it's Tony C. Maybe it's Bill Buchner?
It has to be Johnny Damon then. Put some long hair and a beard on that kid and he's the spitting image.
OK further analysis of that photo, puts it at around 1980-1985, the 90's would have had a rolled brim on any kids hat. So that would make him in his 40's now. Kurt Schilling is my guess.