An acronym of the phrase "raise the jolly roger" used by local baseball broadcasters for the Pittsburgh Pirates following a victory.
The non-abbreviated form would be "Raise the jolly roger" where "jolly roger" refers to the flag design of a skull and crossbones often used by sea-faring pirates. (see Jolly Roger)
It's a fly ball deep to left center and the Pirates make the catch. RTJR! Raise the jolly roger!
A walk-off home run in the bottom of the ninth! RTJR!