I'm with Bankshot.
It isn't Rondo's new "muscle mass": his FT shooting stank even when he "used to be" skinny.
It isn't that the season is new: he's always been this way.
My theory: He thinks he's too cool to practice mundane skills like FT shooting.
Rondo has the skills to be a top player in the league, but he never "turns it on" for more than 10 minutes a game. Why? It's got to be mental, not physical.
Supposedly he did work on his shooting, but he was horrible last night, and he'll never be an above average shooter. I agree with your statement about turning it on for 10 minutes a game. He does seem to be the best player on the court for a short spurt in many games.
working on shooting is not the same as FT's. The motion is completely different. I think his jump shot, from what we've seen looks much improved. Heck, just the fact that he keeps his elbow in now instead of that monstrosity he called a jumpshot the last two years is a vast improvement (realistically speaking of course)
Most good jump shooters are good FT shooters, but it's not a given.
I'm with tommy on this one, he has a horrid FT shot, and im surprised no one has worked with him on it. He shoots his FT from his ear, not above his head and straight on as you should.
Almost every FT he misses is off to the right, which makes sense since he's shooting from an angle. He makes himself do more work than you need to due to that. He has to shoot across his face.