According to MLB.com, Kris Medlen didn't want to throw fastballs to Bryce Harper during yesterday's Nats-Braves spring training game because, well, he's seen what Harper does to fastballs:
"[Gattis] asked me if I wanted to do the Spring Training thing even though Bryce Harper is up there. 'Do you want to just locate your fastball?' And I'm like, 'Hell no.' Because I've seen what he does to fastballs. So we pitched more in-season, mixing up pitches and whatnot. I'm not saying that's how I'm going to attack guys, but I'm incorporating a lot of my secondary stuff."
(Kris Medlen, via MLB.com, 3/5/2014)
It seems Medlen faced Harper once and threw just one pitch; Harper flew out to right field.
(Pic of Harper signing autographs at Spring Training via this YouTube video)