Lincoln Riley says the physical and mental development for freshman quarterback Malachi Nelson since his arrival on campus in the winter has been drastic.

“He’s progressing much, much better,” Riley said after practice Monday. “Physically, it’s been a 180. I would say even mentally too. It was great for him to get the reps during spring. He was probably operating below 50% of his physical capability at that point. We’re glad that he went through it. He’s glad that he went through it. It certainly made him better.”

Nelson had shoulder surgery right at the start of the calendar year, timed to his arrival at Southern Cal. The issue — a torn labrum in his non-throwing shoulder — first appeared during his junior high school season. He played through his senior year and then got things cleaned up with USC’s medical staff.

That meant spring ball was a bit of a wash.

Nelson practiced. And he participated in the spring game as the No. 3 guy behind Caleb Williams and Miller Moss, but he certainly looked like a quarterback who wasn’t 100%. He was charged with a pair of interceptions in the scrimmage.

But a much healthier Nelson gives the Trojans some peace of mind heading into the fall. A year after quarterback depth was a bit precarious, USC finds itself with a deep room.

The reigning Heisman Trophy winner is back in Williams. Moss is expected to back him up once again. USC can bring Nelson along slowly.

A 5-star recruit and the No. 13 overall prospect in his class, Nelson is believed to be the heir apparent at the quarterback spot once Williams heads to the NFL.

Now that he’s healthy, Riley and Co. get to see more of the fantastic prospect they invested so heavily into on the recruiting trail.

“Having three other experienced guys in the room has made (Nelson) better,” Riley said. “It’s a good room. There are a lot of conversations. Guys are competing and they also help each other and push each other. He’s much more confident. High ceiling with him.”