On Monday, he decided to end his recruitment and become a Wildcat.
The decision comes as no surprise, as Kosinski was impressed on a recent visit.
"Two weeks ago I went there and the Arizona trip was fun," Kosinski said. "I got to talk with the coaches and they said they love my game. They like how I finish off blocks and that I play with a little bit of a nasty streak.
"I also got to talk with the players a little bit and everyone just had good things to say. Then I toured the facilities and the campus and everything just blew me away. The visit was informative on about every level."
Kosinski also holds an offer from Air Force and credits much of his improvement to focusing on one sport.
"We're in the process of rebuilding, but we played better this season and I knew I had to elevate my game," Kosinski said. "I thought I did pretty well. I decided this past season to drop rugby and just focus on football and that certainly helped."
Although a few other schools were in the picture, the Wildcats were in the driver's seat as soon as an offer came along.
"They've got pretty much what I'm looking for," Kosinski said. "I'm not a big fan of the whole process. I like hearing from schools and anytime anyone says good things about your game that is great to hear, but I feel I was at the point where I would like to get the decision out of the way.
"I want to focus on getting better and adapting my game to the offense and system that I will play in at the next level."