What do you think Jack would have done had he scene Cal hit Rose ?

Beat him. Plan and simple; Jack would have beat Cal, there's no question about it! He would do anything for her! And we know that cause he gave his life for her:)! And I know Jack wouldn't hurt anybody; but if it was for Rose; he would. Just watch the deleted scene, "Jack vs Lovejoy" and that should pretty much sum up what he'd do to Cal!

He would have gone to Cal and hit in his face... than he would have taken Rose's hand and would have run a way with her<3333333

I think that Jack would have thrown Cal overboard, and then made sure that rose was ok.

If Jack had been in the room with them? I think he would have either punched Cal or thrown him overboard.

I think you mean "seen" not scene.
Well, Jack would probably beaten him but then he'd get caught by Lovejoy and he'd get arrested, unless he's luckily enough to flee with Rose like he did when Cal threatens him by shooting at him with Lovejoy's gun.

I think that Jack would have slapped him. And kick him and then throw him on the wall and say if you touch her again you will die!