An L.A. Dodger fan pulled out all the stops to ask his partner to marry him on Thursday -- running onto the field during the middle of a game to pop the question -- but it might have cost him a few hours in jail ... and perhaps even a night in the hospital.

The wild scene unfolded at Dodger Stadium late in L.A.'s contest against the Arizona Diamondbacks -- when a Mookie Betts supporter hopped the centerfield wall and trotted to the outfield grass.

Video shot by a fan in the stands showed after the man made it to within feet of a D-Backs player, he stopped, got down on one knee, turned to the centerfield seats and pulled out a ring.

But, as he was asking his beau to be his forever lover -- a security guard was having none of it ... and blindsided the dude with a form tackle.

You can see in footage from the scene, the collision was so violent, even Diamondbacks outfielder Lourdes Gurriel Jr. couldn't help but wince.

Two other security guards raced in and piled on the fan ... before he was ushered off the field.

No word yet if he was arrested -- or if he suffered any injuries.

It's also unclear if he left the stadium officially an engaged man ... but after all that trouble, she better have said yes, right?!