Pirates pitcher J.T. Brubaker drilled Nationals shortstop Alcides Escobar in the balls ... in what will go down as one of the most painful pickoff attempts in MLB history.

The wild play went down in the fourth inning of Thursday's game between the Nationals and the Pirates ... Brubaker's throw over to first base hit Escobar square in the groin area.

In the video, you can see Escobar taking a lead off first base when Brubaker turns and fires a throw towards the bag (foreshadowing) that misses everything ... except, well, you know the rest.

Escobar immediately grabbed his marbles as he was falling backward to the ground ... and signaled with his right hand to the first base ump that he needed a few to gather himself.

Play was temporarily stopped (understandably so, if you've ever experienced that pain before) as Escobar rolled around on the ground in clear discomfort.

Fortunately, though, the veteran shortstop was able to laugh about it all as one of his coaches and the team's trainer helped him back to his feet.

Escobar would stay in to finish the game, going 1-for-4 at the plate with two strikeouts ... but the biggest hit of the day came unexpectedly, if you catch our drift.