We have probably seen athletes with two distinct limb sizes, for example Rafael Nadal with his enormous left arm and skinny right arm.
Sanchis-Moysi et al. "Iliopsoas and Gluteal Muscles Are Asymmetric in Tennis Players but Not in Soccer Players" PLoS ONE, 2011.--scientopia.org
Apparently someone has done research on this and came up with the result: tennis players do have asymmetric butt.
To explain this we have to take a look at the anatomy of our butt.
For the gluteal muscles, the soccer players actually showed no hypertrophy compared to normal controls, while the tennis players showed aymmetrical hypertrophy similar to the iliopsoas group, with the gluteal muscles on the non-dominant side 20% bigger than those on the dominant side.--scientopia.org
So, the next time you watch a tennis match, please treasure the opportunity to observe science at work. XD