As the 23-year-old was reaching the bag safely, his iPhone flew from his back pocket ... and hit the base at the same time as he did.
Castro -- who was just called up from the Minor Leagues for Tuesday night's game -- was initially oblivious to it all, but had to pick it up after an ump pointed out to him that it was on the ground. He then handed it over to his third base coach, who didn't appear pleased.
Following the game, which the Pirates ended up losing, manager Derek Shelton was clearly not thrilled with Castro either ... telling media members, "This was just a kid who made a mistake. It’s just one of those things we move forward from and tell him, 'You can’t do that.'"
Castro, meanwhile, said afterward he felt "horrible" about the incident ... and added that it was completely unintentional.
Rodolfo Castro's explanation of what happened with his phone at third base, via team interpreter Mike Gonzalez.
Derek Shelton pointed out that Castro always has his sliding pad/oven mitt, so he probably didn't know he had it. No intent on Castro's part to use his phone in-game. pic.twitter.com/6ujP28VCFG
Of course, outside of the unprofessional look of having a phone out during the middle of playing in an MLB game ... the league has become highly sensitive to technology use in the field of play (thanks, Astros).
Castro seems unlikely to face punishment from the MLB, however ... and if you're wondering why the ball player might be a little tardy getting back to texts on game nights going forward -- now ya know why!