The Phillies took Brendan Lafferty in the AAA part of the Rule 5 draft from the Royals. Lafferty was originally a 47th round pick by the Phillies in 2004, but decided to go to UCLA instead. After 4 years as a mediocre (statistically) reliever, the Royals took him in the 18th round in 2009. He has basically only been a reliever in the minors and the 26 year old pitched the whole year in AA (so he is old for the level).
Lafferty's Pitch F/X data comes from the Arizona Fall League in 2011.
Known for his fastball, it averaged over 94 MPH, along with a lot of sinkers (averaging between 93-94 MPH) and sliders (83.58 MPH average). He also threw a reasonable number of changeups that average just under 80 MPH. When you look at other relievers with similar fastballs, his changeup is much slower than most relievers who throw that hard (which made looking for velocity and pitch comparisons basically impossible). So even though he is not known to have good secondary stuff, he at least throws it a lot. He is somewhat of a sinker/slider guy, but the fastball and change at least gives him some other weapons. Statistically, he doesn't act like a sinker/slider pitcher either. He had a good strikeout rate (25.5 %) with a gigantic walk rate (14.4%) with a mediocre ground-ball rate (and high home run rate) in 2012. He pitched in an extreme hitters park in 2012, but actually gave up more homers on the road.
He also threw strikes under 60% of the time in 2012. 60% is usually considered a magic number that virtually every successful Major League pitcher surpasses (with very few, such as Cliff Lee and Kevin Slowey throwing 70% or near). So, if one is trying to put Lafferty in a category, it is impossible to put him into the sinker/slider category (and is hard to put him in the advanced older pitcher category as well), and instead he falls under the wild/hard throwing lefty.
He has a better K/BB against lefties, along with a better GB %, but his home run rate is higher against righties. This seems to be more of a fluky HR/FB % issue than an actually telling us about his skill set (there are always some issues with reliever splits and sample sizes, even when looking at multiple seasons. Lafferty giving up more homers to lefties doesn't jive a lot with the rest of the information we have).
Lefties that throw hard are always interesting and usually valuable, but the age obviously limits his ceiling. He has the good strikeout rate but Lafferty obviously has a lot of other issues. His delivery is somewhat hard to watch, as he brings his leg up rather high and pauses in the middle of his delivery. His arm slot then seems to not follow his delivery, as he moves his body like he is going to come over the top, only to come what you would probably call 3/4ths. He has good size at 6-3, but it doesn't appear that he is using the size to his advantage and actually looks like he is working against his body while pitching. In much of the video I watched of Lafferty, he was keeping the ball low, but had all kinds of problems with basic command/control. With his velocity and mix of pitches, he shouldn't be giving up homers if he is keeping the ball low. While there is no real way to quantify whether or not he is keeping the ball low (there are technically several ways, but none without flaws such as relying on selection bias, possibly bad stringer data in AA, or just looking at ground-ball rate), it seems safe to assume that a pitcher that throws a sinker at least a quarter of the time but has a 1.34 HR/9IP is not keeping the ball low. I wholly expect that the Phillies are taking a chance on left-handed velocity and will most likely tinker with his delivery in either AA or AAA.