Pain back side shoulder

[big]

Is that the rotorcuff? I have no clue about the different muscles. But it's the muscle behind the delts. I dunno if the delt is just one muscle. It's the one behing the big delt bump muscle thing. And It feels like its over a bone.

[big]

its this muscle posterior (thanks sebi)


I think I got it from behind the neck press, I did them real heavy in the smith. Only got 2 reps. (I warmed up first but it was the first exercise of the day)