Patrick Mahomes isn't a rookie, but he might just be the most fascinating unproven, young quarterback to watch during the upcoming season. After riding the bench behind Alex Smith during his rookie season, Mahomes will finally get his chance to lead the Chiefs during the 2018 season now that Smith finds himself in Washington as the Redskins' new quarterback. 

Recently, CBS Sports Senior NFL Writer Pete Prisco spent time with Mahomes and the Chiefs during OTAs. He came back with an impressive story from Mahomes' rookie season -- a story that he told on CBS Sports HQ on Thursday. 

"He's a kid who's prepared for this," Prisco said. "Last year ... he would go throw after practice. But he wouldn't take any of the first-teamers. The reason being, he didn't want to make it look like he was trying to take Alex Smith's job. That's the kind of kid that he is. He is very, very excited to have this opportunity. And he believes in himself. He played that last game and he said, 'Look, I went back and watched a couple of different times and learned some of things you can and can't do in the NFL.'

"He's got that big arm. He's got the strongest arm in the league probably right now. He's going to take some chances. So you know what he's going to do? He's going to use practice to figure out how and when he can use his arm and get in tight windows."

Mahomes said something similar recently.

"Yeah, him, [offensive coordinator] Eric Bieniemy and [quarterbacks coach] Mike Kafka have really tried to throw a lot at the whole offense," Mahomes said, per Chiefs Wire. "If you want to make mistakes you make them now. You don't want to make those mistakes in the game, so we throw a lot now so when we get to the game it's a lot easier."

There's no doubt that Mahomes' upside is considerably higher than Smith's, which is why the Chiefs traded up for him in the draft a year ago. The thing is, Mahomes' floor is also considerably lower than Smith's, which is why the Chiefs might not be better off in 2018 with Mahomes than they would've been with Smith. 

With Smith, the Chiefs knew what they were getting every year. And pretty much every year, Smith helped the Chiefs reach the postseason. Smith went 50-26 as the Chiefs' starter from 2013-17, but postseason success eluded him, which likely prompted the team to make the switch to Mahomes. It's a move that makes sense and could pay off with a Super Bowl win -- something that's missing from Andy Reid's incredible resume as a head coach. But first, Mahomes will likely undergo some growing pains.

In his lone start during his rookie season, Mahomes completed 22 of 35 passes for 284 yards, no touchdowns, one pick, and a 76.4 passer rating. Those stats don't necessarily stand out, but the footage from that start did.

But again, temper expectations in 2018, which will essentially be his rookie season. Most quarterbacks, regardless of how much promise they hold, struggle during their opening salvo. As Chris B. Brown said of Mahomes last August, "He can do things that help you win championships, but he still has to learn to do the things that get you to the playoffs." 

That's what this season is all about. But once Mahomes learns those things, he'll likely take off and carry the Chiefs with him.