Originally Posted by Sid_Vicious
Not lack of speed. I think it is due more to lack of agility. There are some Tall players that can get from point A to B very quickly, but their big frames prevent them from changing directions laterally.
And they also tend to be worse at moving forward to lower balls. Del Potro often amazes at how well he handles low, short balls with such a big swing but, in the long, it's more difficult for them. The longer a match or slower the court, the more movement shortcomings get highlighted.