Tapia is a fun prospect. He's huge, with a loose, easy arm that generates a plus-plus fastball. He was regularly 94-96 with plenty of 98 and 99 mph in 2012 with Savannah. It's not straight either. He gets sink on the two-seamer and armside run if it's up.
During the 2012 season, he started added a four-seamer (also in the mid-upper 90s) to work away to righties and in to lefties. Alongside Zack Wheeler's heater, it was the best fastball in the system last year.
His primary off-speed pitch is a change-up at 88 ish mph. He throws it with good arm speed. At times he gets really good tumble on the pitch and it almost acts like a splitter or even a two-seamer if he turns it over. If it's up however, it's a fat (slow) meatball.
Tapia could probably survive, or even be very effective out of an MLB bullpen with his two fastballs, and more consistent action on his changeup. However, he's rough around the edges - he has trouble holding runners at first and can be awkward fielding his position at times.
Tapia throws out a very low arm slot and struggled with his slider in 2012. I tried to capture the low arm slot standing behind him in spring training. In the frozen frame at right, you can see the arm is almost straight out to the side from his shoulder and his hand is not much higher. That's really low. At times he would baby his slider, and it would be soft. If he picked his arm slot up to get on top of the pitch, it just looked very different out of his hand than his fastball. So, if you're really looking for something out of Tapia today, enjoy the gas, but see if he can throw a slider for a strike.