See the links below for the rest of my AFL scouting notes.
A very patient hitter, Decker has good pull-side power. His biggest strength is also his biggest weakness. He'll take four pitches in a row at times, waiting for a pitch he can crush. Others, he'll come out hacking and end up expanding the zone. It's an approach that lends itself to a lot of walks, some streaky power and a high strikeout total. On the plus side, Decker can "trick" pitchers into throwing his pitch. The down side is that he's not a good enough contact hitter to be able to fall behind in the count.
Anyone who labels Decker as a well-below-average defensive corner outfielder is lazily looking at his build and pretending that they saw him play. He's surprisingly fast with a very strong arm and solid instincts in the outfield -- he's a bit of a pest on the base paths, too. It's unlikely that he's more than an average defensive corner outfielder over the life of his career, but he's far from a liability out there.
While he has been very young for his level, Decker is a guy who minor league pitchers have been able to shut down at the plate for extended periods of time. I'm not sold on his approach translating well to the majors, though he's a candidate to arrive with his hair on fire his first time through the league. I see a potential average corner outfielder over the life of his career who will primarily reach base via the walk and have some extended slumps. Throw in that he may be spending a lot of time in Petco Park and he's not the greatest bet to surface as an impact hitter.
Follow Adam on Twitter @AdamWFoster.