Stat your case: 49ers units as a concern

Each week, the Stats & Information Group will look at a noteworthy discussion topic and debate the possibilities that come from it, using data to back up their points.

This week’s topic is “which 49ers unit is more cause for concern - the offense or defense?”

The Offense

While the 49ers defense hasn’t been the same unit as the one that has ranked in the top four in terms of expected points added allowed over the past two seasons, it’s the offense that is the larger issue.

The loss of Michael Crabtree to a preseason injury has seemingly unhinged the unit. Once Colin Kaepernick took over as the starter in Week 11 of 2012, the 49ers had only two games for the remainder of the regular season where their team offensive EPA was negative (Week 13 at Seattle and Week 16 at Seattle).

After a stellar game against Green Bay in week 1 this year, the offensive unit has cost the 49ers nearly 28 expected points in the two games since, the worst offensive EPA in the league over the last two weeks. This has been mostly due to turnovers and setting the defense up in bad field position.

A large contributor to the 49ers’ negative EPA on offense has been turning the ball over. Over 17 percent of the 49ers offensive drives this season have ended with them turning the ball over, ranking the 27th in the league (league average is 12.7 percent). This coming just a season after turning the ball over on 7.3 percent of their offensive drives with Kaepernick as a starter in 2012.

Their failure to come up with a sustainable offense that contributes points to the scoreboard rather than taking them off, combined with their inability to retain possession of the football, is the 49ers larger issue.

--Hank Gargiulo

The Defense

The 49ers defensive unit has struggled so far this season and is the main reason why San Francisco is off to a 1-2 start.

Last season, the 49ers defense allowed 17.1 points per game, second only to the Seahawks. This season, the ‘Niners are allowing 28.0 points per game, the eighth most in the league.

The 49ers have allowed a league-high 14 drives to reach the red zone this year, 10 of which have resulted in touchdowns, which is also the most in the league. They allowed 22 such scores during all of last season.

Unlike last year, the 49ers have been unable to shut down opposing rushing games. In 2012, the Niners allowed the fourth-fewest rushing yards per game (94.2) and the fewest rushing first downs per game (4.5). This season, San Francisco ranks 29th in opponent rushing yards per game (139.7) and is tied for 29th in rushing first downs per game (8.0).

Another issue has been the uncharacteristically undisciplined play on the defensive side of the ball. In Jim Harbaugh’s first two years as head coach, the 49ers averaged 2.3 defensive penalties per game. This season, they have 13 through the first three games (4.3 per game). Only the Detroit Lions have more.

It will be difficult for the 49ers to turn their defense around significantly at this point, especially with All-Pro linebacker Aldon Smith out for an undetermined amount of time.

--Mike Bonzagni