Entering into the 2014 NFL Draft the St. Louis Rams had one of the best defensive lines in the NFL. Still, the Rams decided to draft Pitt defensive tackle Aaron Donald with the 13th pick. It's a way to take their defense to the next level. A team can never have enough pass rushers, so the Rams decided to feed the beast.
Donald was a special prospect, and he should be a special player. The only real question mark in regards to Donald is that some people feel as though he is too small. Many teams would rather be safe and have big defensive tackles But there's no reason to assume that Donald won't succeed for the Rams. Many people compare Donald's ability to Geno Atkins, who is a hell of a defensive tackle.
The reason why Donald is a special prospect is because of his ability as a pass rusher. There aren't many defensive tackles that have the speed and athleticism to beat guards like he does, and, damn, can he use different techniques well (read what former NFL defensive end Stephen White said about him). He could end up overpowered by guards in the run game early in his career, but even if that's the case, he's still valuable because this is a passing league.
The Rams have a packed defensive line with Donald added to the roster. Obviously the the starting four defensive linemen for the Rams are Donald and Michael Brockers in the middle with Chris Long and Robert Quinn on the outside They also have backup defensive ends William Hayes and Eugene Sims, who have been important and productive role players. People tend to forget that the Rams added another pass rushing interior lineman in free agency this spring in Alex Carrington. He last played for the Buffalo Bills last season, missing all but three games because of a torn quad.
Being a starter for the Rams defensive line doesn't mean much because of the frequency that the Rams rotate players during games. Donald will get plenty of playing time, and he could end up with most of the snaps out of the defensive tackles. He will eventually be the "official" starter this year or next year, but there's honestly no reason to rush him. The current starters, Kendall Langford and Brockers, have played well. Adding Donald gives the Rams a much needed penetrator to press the pocket from the middle.