At times, the Rams defense looked like the best unit in the league in 2014. They held Peyton Manning and the Broncos offense to 7 points in Week 11. They posted back-to-back shutouts against the Raiders and Redskins a few weeks later. Still, at other times, the Rams were not very good. They allowed 30 or more points in 7 of their 16 games. Despite all of the talent on their roster, they finished as a middle-of-the-pack defense in points and yards allowed. So what was the reason for the inconsistency?

Top to bottom, the Rams were and are among the most talented defenses in the NFL. Robert Quinn has established himself as an elite pass rusher who has to be accounted for by the offensive line at all times. Defensive tackle Aaron Donald had a tremendous rookie season in 2014, registering 9.0 sacks and splitting double-teams with regularity in the running game. The Rams had talent and speed at linebacker, as well as safeties and corners who were aggressive tacklers. As a unit, the Rams defense flew around the field last season.

Defensive Coordinator Gregg Williams implemented his system of aggressive blitzing and disguise. At their best, the Rams were able to combine a fierce pass rush with coverages that confused even the best quarterbacks in the game.

The below play from Week 11 against the Broncos was a perfect example of this. This was 4th-and-4 with just under 10 minutes remaining in the 4th quarter. Denver desperately needed a conversion. At the snap, the Rams looked like they were playing man free (man-to-man coverage with a free safety in the middle of the field). It appeared as though they were matching up as the picture below shows.

After the snap, the defender who appeared to be covering the #3 inside receiver jumped inside of Wes Welker. The defender over Welker, jumped outside of him.

In effect, these two defenders were bracketing Welker. They baited Manning at the snap by making him feel comfortable that he could get Welker in 1-on-1 coverage right around the first down marker. Instead, Welker was double-teamed. Manning recognized this after the snap, but by then it was too late. The Rams had gotten inside pressure with a blitz, and the result was a sack.

This basically ended the Broncos chances of winning that game.

The Rams aggressiveness and disguise were part of what made them a good defense last season. Their unconventional coverages created hesitation by quarterbacks, and their blitzes created mistakes. The Rams were near the top of the NFL in blitz frequency, sacks on blitzes, and interceptions forced on blitzes.

So with all of that great talent and scheme, why were the Rams so inconsistent? Well, there are a few reasons.

Teams were able to use the Rams’ aggressiveness against them. In Week 12, for instance, the Chargers had lots of success using screens, which got ball carriers out in the open field past blitzing defenders with more space to maneuver. This could be one reason why the Rams allowed the 7th most yards after catch in the NFL last season. It could also explain why the Rams ranked 22nd in opponent passer rating vs. the blitz.

Another reason for the Rams’ inconsistency was discipline. There are times to be aggressive, but there are also times to play to your responsibilities as a defense. The Rams secondary was great at attacking running backs in the running game, and at pouncing on receivers. Sometimes that aggressiveness backfired, though.

Take this play, for instance. This was 1st-and-10 and the Rams played Tampa-2 coverage. The Chargers ran a dig-flat route combination that attacked cornerback E.J. Gaines, who was playing inside.

Gaines, who impressed all season with his ability to come up in the running game, pounced on the flat route after quarterback Philip Rivers gave him a bit of a shoulder roll.

He abandoned his zone responsibility and left a gaping void behind him.

Why did he do this? If the running back had caught the ball in the flat, cornerback Janoris Jenkins (who was playing to his responsibility) was there to make the tackle. Gaines could have then come up to help and ensure it was only a short gain. His aggressiveness got the best of him, and it created an easy 14-yard completion for the opposition. Gaines knew it too, as he put both his hands on the top of his helmet in frustration after the play.

This play against the 49ers in Week 6 was another example of over-aggressiveness. Here, the ball was snapped with 24 seconds left in the half. The 49ers had 80 yards to go. The Rams rotated to a cover-3 defense after the snap. Gregg Williams even got a little fancy and had his middle linebacker, James Laurinaitis, drop back as the deep middle defender instead of a safety. The two deep safeties at the start of the play jumped underneath.

Cornerback Janoris Jenkins was responsible for the deep 3rd of the field to his side. Yet when receiver Brandon Lloyd gave him a double-move, Jenkins jumped it and got burned. Below, you can see him starting to squat on the route.

And now you can see Lloyd running by him.

The result was an 80-yard touchdown right before the half. Why did Jenkins try to jump this route? A 12-yard completion there does nothing to hurt you as a defense. Not to mention, as an outside corner in cover-3, you’re responsible for the deep third of the field. Jon Gruden, who was calling the game on Monday Night Football, even cried out after the play, “That is horrible defense by St. Louis!”

By design, the Rams secondary wants to be aggressive and jump routes. They don’t play a lot of man press coverage. Normally, they play soft coverage and sit on routes expecting quarterbacks to get rid of the ball quickly in the face of the blitz. They’re pretty good at this in general. However, if the pass rush doesn’t get there in time, it sometimes leaves the secondary flat-footed and susceptible to big plays over the top.

The Rams have most of their talent returning on defense in 2015. They’ve added depth to their defensive line and linebacking corps in Nick Fairley and Akeem Ayers. They have a serious chance to compete in a very tough NFC West. If they can eliminate the mistakes in their 2nd season under Gregg Williams and gain more consistency (and if the offense can start pulling its weight), they should be in the playoff mix in 2015.