Hmm.....
I tend to disagree.
I was a multi sport athlete in High School and am now a coach.
Kid is not going to be a very good hitter if he only hits in the spring and summer, I took BP and threw (to keep my arm in shape) during football and basketball season.
Kid is not going to be a very good QB, WR or DB if he only throws passes, runs routes or covers receivers in the fall or during a few 7 on 7 games after baseball is over.
And a kid is never going to be good shooter of the basketball if he only shoots during the basketball season.
Skills are honed, not mastered, they need to be developed and practiced repeatedly.