Scott Hairston was traded by the Cubs to the Nationals for minor league pitcher Ivan Pineyro. Hairston wasn't playing full time for the Cubs and was really struggling when he was playing.
I'll only looking at his data against left-handed pitching, because that is all that really matters for him. He is a lefty masher, just a platoon player for the most part, with large platoon splits in his entire career. In his small sample size with the Cubs, his overall OPS against lefties was still okay because he still hit for power. I did want to see if there was a skill set or approach change, so let's look at his average locations along with average velocities of his results.
This year with the Cubs:
It appears to me that he is still handling hard pitches just fine, but is having more problems with off-speed pitches. He was really just a hard ball hitter with the Cubs for the most part, which is also shown by the difference in location for his 2013 whiffs. He was also just pitched more low and away as a whole when he was with the Cubs, as teams seemed to take advantage of his aggressiveness. To me, this is more encouraging than the opposite (still hitting off-speed pitches the same but regressing against fastballs, like it appeared he did last season) because it still implies that he has bat speed, that is, unless he is just cheating on balls badly. The power is still there, so even if he is a binary hard ball hitter going forward, he'll still be useful as a pinch hitter in the National League.
Ivan Pineyro is a 21 year old right-handed pitcher originally signed by the Nationals out of the Dominican Republic. When I watched him pitch online, he looked lanky despite being 6-1.
The release point seems to come quite a bit out, a more than average 3/4ths delivery. Mechanically, he has a lot going on, with a lot of leg and arm motion in the middle of his delivery. It hasn't led to high walks rates though, so as long as he controls it, it probably doesn't really matter (I don't think it helped with deception).
His fastball is probably average at best when it comes to velocity, but I didn't hear a lot of readings. He seemed to keep the ball low, so I am surprised he is not an extreme groundball guy. He threw a lot of breaking balls, even in the first inning, showcasing a 76 MPH curveball. He liked to use it and a few changeups against lefties. Against right-handed batters, he can sweep a slider away, but the break isn't hard, somewhat slurvy.
The outing I saw was when he was in A-ball, and it was pretty clear that he was ready for another level. The Nationals agreed (the numbers backed it up as well), sending him up to A+ before the trade. Pitchers without huge fastballs below AA are really difficult to evaluate, especially when it comes to comparing to a MLB player. The problem is compounded, I think, when the player wasn't subjected to the draft. It makes them harder to peg when it comes to value. You can point out that Pineyro has potential, having professional success at a young age (that is, most college guys who were drafted are older than him, and you can probably count the ones ready for A+ success on one maybe two hands), but that is really vague and not helpful. He is the type of flier arm that I don't think the Nationals mind giving up for a player that can help the team now.