De La Rosa is a 30 year old right-handed reliever who had 12.1 career big league innings before 2013, all with the Rays. While De La Rosa had two straight successful and high strikeout seasons with the Rays AAA club in 2011 and 2012, he had spent 2005-2009 in independent ball after not reaching full season ball with the Yankees. Before the start of the 2013 season, the Rays traded him for Steven Geltz, which said that he had some value, which I found really surprising at the time.
When I watched and took notes on De La Rosa last year, I thought his fastball was rather uninspiring. His fastball was really below average out of the bullpen when it came to velocity. With the Angels, it has been anything but, averaging over 94 MPH. Maybe the minor league gun wasn't working properly that day, or maybe he was just having a bad day (if nothing else, it is a cautionary tale on one time looks), but the fastball is good velocity wise. This certainly helps (no one on the above list didn't throw hard), but he is not in the top 10 in fastball velocity but is in the top 10 in fastball whiffs. Vertical movement tended to be a good indicator as to why some plus fastballs got whiffs and some didn't, and De La Rosa gets a lot of vertical movement on his fastball according to Pitch F/X (nearly a full inch on average better than the average whiff on 95 MPH + fastballs). The Angels' ballpark does make vertical movement data higher apparently, and it shows when you break De La Rosa's vertical movement data by home and road (at home it is around 11 inches, on the road it is about 9 inches). With this correction, he is in more human territory, but still in good territory.
Still, it is helpful to look at location to see if we can get an idea of how he is pitching and how the approach with the fastball is helping him succeed. The following graph is all the fastballs he has thrown so far this season.
It seems that he is working both high and low, with a lot of fastballs on the glove side.
Here are the average placements of his fastball, both on a whole, and sorted by result, with the average fastball location in his short time as a Ray included for reference (this entire graph is the strike zone)
There hasn't been a major release point change, but there has been a full MPH velocity change, going up from 93 to 94 MPH. Why he suddenly gained velocity on his fastball at age 30 is unclear. Perhaps there was some delivery change that allowed him to get the ball more glove side and throw harder, but at the same time, release the ball from basically the same point. Whatever happened, De La Rosa appears to be for real, and he was a really good acquisition by the Angels, a team always looking for help at the back end of their bullpen.