Every now and then, I bump my leg on my back swing.  What's off? 

not giving us much to go one......when does it hit? on the way down in step 2? on the way forward in step 5? when youre playing straighter? when youre hooking it a ton?

In theory, the ball should be going down on step 2 instead of 3.  The ball should be going into the back swing along with your 3rd step going forward (or following your 2nd step back).

At the end of the 4th step, the ball should have already gone as high as it is going to go in your back swing.  5th step goes forward along with the ball.  I am betting your are still going into your back swing at the beginning of your 5th step and having to force the ball into the swing with late timing.

I'd be willing to bet it's the direction of your footwork.  Steps should be directly in front of each other.  The first "cross over" step creates a path for the ball to swing close to the body without hitting the leg.

The more I think about it, I bet you are on the right track.  But I still wonder if he is dropping his ball down on his third step, and hitting his leg, then I can only imagine.  Not often I see bowlers hit their left leg going to the back swing when they are right handed.