As always, basics first. Clarkin is a 6' 2" 190 lb Left Handed Pitcher from San Diego, CA. He is a commit to University of San Diego (that had a crazy good recruiting class that will likely lose many to the First Round). For his repetoire, Clarkin currently has a potentially plus Fastball, a potentially average to plus Changeup, and a flat out filthy Curve that has plus-plus potential. Scouting reports are somewhat mixed as some think he's maxed out physically for his frame and others think he can add 15-20 pounds and gain 2 or 3 MPH on his fastball. That's a huge difference. A guy with his fastball in the upper 80's/low 90's probably maxes out as a #2 Starter. A Lefty with a Fastball typically working at 95 and maxing out at 97-98 mph is almost certainly an Ace and one of the best starters in baseball (assuming improvement in his other 2 pitches and development of a show me pitch).
So what does this kid look like? Let's go to the video. Lots of effort in the video below from Perfect Game. The high leg kick looks familiar and the high hand placement scouts like as it improves his deception. He throws from what looks to be a 3/4 arm slot and his mechanics look a little inconsistent, which has also been noted by scouts. It's not anything scouts seem to see as a red flag, more just minor tweaks to iron out those differences. Otherwise, this is a bad angle video and you can't see any pitch movement, so on to the next video.
This is another Bullpen Banter video. We can see better here that, much like Rob Kaminsky, Clarkin comes down with his foot to the first base side of the mound and throws across his body a bit. Sometimes his foot points toward the first base line and he sometimes hops at the end of his delivery. Those foot turns should be a minor fix, though he'll likely keep throwing across his body some.
Here's an older Bullpen Banter video of him from the Perfect Game All America game last summer. This is largely more ofthe same as above, but it can be fun to watch what these kids do, in the event you draft one of them.
So what does this all come down to? Well scouting reports uniformly praise his Curve, note he may have an above average Fastball and his changeup is pretty advanced for a High Schooler. His control is inconsistent (mostly due to equally inconsistent mechanics). Anytime there's a question about mechanics and control problems, well some of those guys never figure it out, even for minor fixes. His ceiling is somewhere between Cole Hamels and Jon Niese (quite the range). He's either maxed out physically, or he'll grow 15-20 lbs. If his ceiling really is Hamels, I'd take him mid-teens, sure. If he's Niese? Meh, I'd rather go for a high risk guy and hope for the best.