This past Monday, against Cleveland, Seattle left-hander James Paxton recorded the highest single-game average fastball velocity of his career, at just under 99 mph. While sources differ on the matter, it was at least a mile per hour harder than his previous single-game high, which he’d established in his previous start (and season debut) at San Diego about a week earlier. Jeff Sullivan described that appearance against the Padres as “horrible and promising,” because Paxton had allowed eight runs in just 3.2 innings, but also exhibited a sort of arm speed he hadn’t previously. Monday’s start wasn’t horrible, at all. And even more promising.

There’s a mechanical explanation for why Paxton threw harder on Monday than he’d ever thrown before. But there’s also a change in pitch mix that led to one of the best starts of his life, too. And with those new mechanics and that new pitch mix also came a new mindset. It might be fair to say this is a new James Paxton.

Triple-A pitching coach Lance Painter suggested a change in arm slot to the lefty. “I was getting way too high on the front side,” Paxton told Shannon Drayer. “It wasn’t a point of strength for me to throw from. Paint didn’t think it looked right.”

The coach had Paxton pick up the ball and throw to first base to illustrate his natural arm slot. Pitchers can often get so wrapped up in their own mechanics as a pitcher that they forget how they would naturally just, you know, throw the ball. A simple throw to first unlocked his most comfortable mechanics.

“It just feels natural coming out from that slot,” Paxton told Drayer. “I was just working on getting everything on target and staying through the glove instead of to it and it worked out really good.” So check out the drastic change in his velocity paired with the drastic change in his arm slot.

Lowest arm slot of his career, biggest fastball of his career. Not surprisingly, Paxton is in the midst of the best two-game stretch of his career when it comes to fastball whiffs.

But Paxton had this velocity, mostly, in San Diego, and he gave up 10 hits in less than four innings. Monday against the Indians, he only gave up five hits in six innings, recording 10 strikeouts against one walk. Those are numbers he’s only bested once before in his career.

Another thing Paxton did Monday was throw the slider (sometimes classified as a cutter) a ton. He threw 26 of them, eight more than his previous career high. Those sliders featured the best combination of velocity and drop of his career. He got seven whiffs on the pitch, three more than his previous high, which was set in San Diego.

Here’s the slider in 2015, a side-to-side pitch from his old, higher arm slot.

Here’s the slider in 2016, with more drop from the new arm slot.

Maybe finding an arm slot and throwing harder and throwing more hard breaking balls was all that Paxton needed to unlock his potential. That’s what he did in San Diego, before amplifying the effect even more in Cleveland. The two games were close in that respect, if not in terms of outcomes.

There’s another part of his approach that changed with arm slot. Again, from Drayer’s post:

To illustrate the point, Painter had Paxton field a ground ball and throw it to first base. That, he told Paxton, was his natural arm slot. Paxton discovered that once he was able to repeat it, he had more success hitting the inside corner, which opened up the outside for him.

Eleven times in his past 32 starts Paxton had hit the inside corner to lefties more often than he did Monday. So his use of the pitch on the inside wasn’t unprecedented. However, never before had he hit the outside corner with his hard breaking ball as often as he did Monday. So the reward ended up being more impressive than the work he had to do inside to get there.

There was one last change that the Mariners asked of their lefty. “I’ve always been an internalizer and didn’t really show a lot of emotion and he wanted me to show a little emotion today, so I was trying to let that out a little more,” Paxton told Drayer.

I may be connecting two dots that are far apart here, but that sounds like Paxton accessed his adrenaline better and had more intent behind his pitches. As Kyle Boddy (and Paul Nyman before him) has stated previously, you have to try hard to throw hard. Intent can be as important as fitness.

So the overhaul for Paxton was really a complete one that reached from his mechanics into his approach and even required a mindset change along the way. The Mariners always knew they had a talented lefty with a big arm before, but now he has three legit pitches and more of a bulldog attitude. Health willing, baseball should expect more of this from James Paxton.