Beat him. Plan and simple; Jack would have beat Cal, there's no vraag 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!
I think u mean "seen" not scene. Well, Jack would probably beaten him but then he'd get caught door Lovejoy and he'd get arrested, unless he's luckily enough to flee with Rose like he did when Cal threatens him door shooting at him with Lovejoy's gun.