Rashi: Is it small for you, that the strong among you graze [in] the good pasture ? if only you would not trample the rest with your feet, and the rest of My flock could eat it! Rather, the rest [of the pasture, that you do not eat] you trample with your feet. And it is not enough for you that you drink the clear water ? you muddy the rest with your feet!

Rashi citing Targum Yonasan: Is it small for you, that you get good sustenance ? the excess [that you do not eat], you thresh (trample) it with your feet! And you drink good drinks, and the rest, you thresh it with your feet!

Rashi: It is clear water, that the mud sank; it was not clouded via feet.

Radak (19): This is trampling water and making it cloudy; the same applies to Mirpas (19).