The first two innings for Arrieta were completely dominant, he got 2 strikeouts, 2 groundouts, an infield fly-out and a fly-out to center.
Average velocity on all pitches: 91.51 MPH
Fastball/Sinker Velocity: 95.76 MPH
As you can see, he is throwing mainly glove side here, away from righties, in to lefties.
Release Point Consistency: Standard Deviation was .182 horizontally and .084 vertically
Release Point Averages: 6.54 vertically -2.3 horizontally
The 3rd inning was very shaky, as he walked 3 batters, gave up a run, and struck out two swinging.
Average velocity: 92.78 MPH
Fastball/Sinker Velocity: 95.06 MPH
Standard Deviation was .164 horizontally and .085 vertically
Release Point Averages: 6.43 vertically -2.36 horizontally
In the 4th, it looked like he had put it back together, with 2 strikeouts, and a groundout.
Average velocity: 90.9 MPH
Fastball/Sinker velocity: 94.21
Standard deviation was .142 horizontally and .085 vertically
6.43 vertically -2.29 horizontally
In the 5th, the wheels came off. He walked a batter, plunked a batter, walked another one, then gave up a single. His day was done, with no outs recorded in the inning.
Average velocity: 89.75 MPH
Fastball/Sinker velocity: 93.78 MPH
His strike zone:
He actually continued to work more glove side, but there is a few more pitches left up.
Standard deviation was .14 horizontally and .071 vertically.
6.35 vertically and -2.46 horizontally.
So he wasn't more inconsistent with his delivery, he just dropped down as he struggled (or struggled because he dropped down). I wanted to see if this was visible by screenshots. The one on the left is not from the Dodgers game, but represents a 6.51 vertical release and -2.35 horizontal release, basically what he was doing in the first two innings (I used that instead of one from the Dodgers game because he was wearing 42 for Jackie Robinson day in this one, which helps show the difference), while the one on the right is his last pitch against the Dodgers:
His velocity also regressed badly as the game went along, as you see. This raises a chicken or the egg question. Was his velocity regressing because his arm angle came further out? Or vise versa?
It also causes one to speculate. Is he tired? Is he hurt? Why did he "wear down" so quickly? Is his delivery simply too hard to repeat? It doesn't appear to be particularly violent, but is it really just putting too much strain on him? Is he yet another Orioles starting pitcher destined for relief? If he keeps breaking down in games like he did on Sunday, the Orioles may ask him if he can just throw 100 MPH bullets out of the pen (a bullpen that doesn't have a lot of room in it).