A fun day at the ballpark turned into a nightmare for one Home Run Derby volunteer on Monday night ... because as he was trying to help shag balls at the MLB's pre-All-Star Game event, he got drilled in the face by a Vladimir Guerrero Jr. line drive.
The scary incident happened during the final round of the showcase at T-Mobile Park in Seattle ... when Guerrero Jr. was trying to put up a big HR total to beat out Tampa Bay Rays outfielder Randy Arozarena for the event's trophy.