Technical Flaws in Pro
Two Handers: John Isner
If you watch John Isner play live or on TV you cannot help but see the difference in the shot quality between his forehand and his backhand. Occasionally he hits a two-hander that looks ok and seems solid or even effective but you frequently see him make horrendous errors, or see the stroke just disintegrate.
The high speed video makes it clear why. The reason is the most fundamental component of every stroke--grip. In Isner's case, the problem is his grip with his bottom, right hand.
Although Isner does shift his bottom hand upward from his forehand grip, he never makes it to even a mild backhand grip. Not even as far as his grip when he hits a one-handed slice.