Take 10 guys with average athleticism who have played neither basketball nor tennis in a year, put them on a court, and in 30 minutes they'll be playing reasonably well. Pick any two of those same guys, put them on opposite ends of a tennis court, and you'll swear they'd never played tennis in their lives.

Oh, and one more thing. Don't let a big 6'6" football player marry a 6'1" basketball player. If they have a daughter she'll be huge and undateable to 97% of the male population.