Yes, backhand gets wonky on the balance.
yea true. i only comment on 1hbh's though.
Ok, your fh...
Looks pretty good. You've got all the good elements going on in there. I hope I can explain this in an intelligible manner...
As I was watching your fh I couldn't help but notice something was 'off'. Took me a while to pinpoint but then I figured out that it was the end of your swing on the follow through that looks funny. If a follow through looks funny then that means something else previous to that was the culprit right? You've got this nice setup, some ssc action, good contact, everything looks good and then it sort of dies at the very end.
The issue is the left arm and the effect on balance. I've had this same issue before w/ the same symptoms and a former world class junior gave me this tip and fixed me up. (this guy has beaten berdych when he was 16).
Now I know what you're thinking, "yea whatever. cheetah is gona give me the usual schtick about the left arm that I already know...".
But this is a little different.
I can see that you know to use the left arm but there are a lot of times when your left arm does not pull over and it's left across your chest and you get the arms-crossing thing. Other times the left pulls across but it's not really 'doing anything'. kind of just going along for the ride. These 2 situations affect balance. balance is king.
Your fw is good, setup is good, initial balance is good, swing path and point of contact, extension all good but the left arm is left picking up kinetic scraps or getting in the way. Why is that? The reason is because you're doing it, excuse me here,.. wrong. There is a better way. The way you are doing it does not contribute to the swing and goes against balance during the swing therefore your brain is saying 'wth? i don't like this. why are you forcing me to do this?'
The Fix:
You need to bring the left arm across in a way that maintains balance and symmetry. I'd bet that currently when you think about the pulling the left arm over you are thinking something along the lines of 'pull the left arm in'. So if the left arm was pointing to the side fence parallel to the baseline and you pulled it in it would follow a path roughly parallel to the baseline. Am I right? That's why you get the arms crossed sometimes. it gives up after a certain point and just lays there. So you have your torso's center of mass, a right arm extended out to the right of the body and a left arm just dangling there. Bye bye balance.
What you need to do is instead of pulling the left arm 'in' -- is to think more along the lines of 'pulling it over'. Not a straight pull across but more of a 'pull over and around'. You have to mimic the position of the right arm. You can do this by giving more abduction to your shoulder on your left arm. (more space between the arm and body, elbow extended away from the body)
Look at Fed in this segment in the following vid:
http://www.youtube.com/watch?v=xDJJS3d2N1c&t=6m48s
See how his left arm is in a similar position to the right arm? Notice how natural and balanced and powerful that looks? He has more shoulder abduction in the left shoulder than you. It's the same amount as his right arm, same angle. Left elbow is away from the body.
Notice that all good players have this 'square box' look.
Safin:
http://www.youtube.com/watch?v=StVULV2N3l0&t=5s
Roddick:
http://www.youtube.com/watch?v=V-D32RwsD_w&t=10s
Djoko:
http://www.youtube.com/watch?v=Gq09yHPmKh0
Verdasco:
http://www.youtube.com/watch?v=bkyL5XF1QO4
Blake:
http://www.youtube.com/watch?v=rAyQ0eP0Eh0&t=44s
Kohlschreiber:
http://www.youtube.com/watch?v=rAyQ0eP0Eh0&t=1m22s
Nadal:
http://www.youtube.com/watch?v=inQvbT8uEGk&t=25s
Henin:
http://www.youtube.com/watch?v=KBioEMX2IdM
Agassi:
http://www.youtube.com/watch?v=cnnKt_SeJ6s
Their arms and shoulders move together as a unit. It looks like a machine. Their chests looks expanded. Yours looks collapsed.
If you grab a racquet and shadow swing this movement you're going to feel a difference right away on the 1st swing. It will feel 'right'. You'll also notice that at the contact point you will feel more stable and balanced. The body won't feel tugged off balance which you probably didn't notice before but you will now when you see the difference.
One thing this method gives you in addition to better balance, is more power. You will feel that your left arm now plays a more active role in the swing. You will feel both of your shoulders are now engaged instead of just the right shoulder. Also you will see that with the correct pull of the left arm in this position that it will stretch your pectoral and shoulder muscles. This stretch will give you more rhs.
You will also notice that the entire swing feels better.
Also once I learned this I found that it was instantly incorporated into my swing. I didn't have to work on building the muscle memory for it... as if my brain approved, was happy, and picked it up right away.
Give it a try with some shadow swings and you'll see what I mean.