A homeless man charged with shoving an off-duty NYPD cop onto Manhattan subway tracks was once a standout Big Apple high school hoopster — until his life went off the rails.

Aaron Walker, Jr., 28, was on his way to a promising basketball career at Cardozo High School and a freshman start at Manhattan College until he disappeared into the streets — and now has 18 busts on his rap sheet and an attempted murder charge in the cop-shoving incident, The Post has learned.

It’s a tragic fall for a young star once nicknamed “Skywalker” for his hardwood prowess. 4

“Aaron was known for getting in the lane and throwing down some crazy dunks, which gave the team and the gym crazy energy boosts,” former Cardozo teammate Rashond Salnave told The Post.

“We were one of the better teams in the ci

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