ABANDONED. Boy helps baseball player in batting slump by noticing his stance has changed - read in 1970s

[Emily]

It's about baseball. It is about a boy that helps a player who is going through a batting slump. (view spoiler)[ The boy watches the player on TV and notices that the player’s batting stance has changed. The boy used to be able to see the player’s number when he was at the plate and then he couldn’t. The boy writes the player a letter and “saves the day!” (hide spoiler)] Does this ring a bell with anyone?

[Bryan457]

I read pretty much zero sports themed stuff, but there is this author who writes sports fiction that is always in the Juv. section of the library.
Mike Lupica
It might be one of his books.

[bookel]

Could it have been something by Matt Christopher?

[Lobstergirl, au gratin]

Emily has left the Group so moving to Abandoned.