Colin Kaepernick has taken the brunt of the criticism for San Francisco's struggles, which may have peaked Thursday night when the 49ers were manhandled by the Seahawks at home.

The quarterback was sacked six times and failed to throw a touchdown in his fourth game this season.

But why was Kaepernick such an easy target back there?

"Because they didn't block anybody," said three-time Super Bowl winning offensive lineman and current ESPN analyst Mark Schlereth on SportsCenter Friday. "It's endemic, to play great offense, you've got to actually block people. You've got to actually control the line of scrimmage.

"In 12 years of playing, and 15 years of broadcasting, it's the worst I have ever seen an offensive line play consistently across this league. It's pathetic."

[MAIOCCO: Kaepernick sacked six times by Seahawks, sustains hand injury]

It was bad. Only two 49ers offensive lineman finished with a positive grade, per Pro Football Focus, and barely. One was tackle Joe Staley (+1.1) and the other was center Marcus Martin at +0.2 (second positive grade in 15 career starts). 

Alex Boone was graded at -0.9, which would have been positive if not for two holding calls. Right tackle Erik Pears (-5.1) and right guard Jordan Devey (-3.7) continued to struggle immensely, allowing most of the pressures. 

"It was awful last night," Schlereth added. "It was an exclamation point on how pathetic the San Francisco 49ers are.

"'Oh Colin Kaepernick, it's time to move on, he can't play.' Stretch Armstrong couldn't play behind that line of scrimmage right there. I don't care if you're a super hero, you're not doing anything behind the way they played last night. They should be embarrassed ... C'mon, clown. Block somebody."

 

[RATTO: Bad 49ers never competitive, lack any workable foundation]

On the season, three players on the 49ers offensive line are among the worst in the entire league, according to Pro Football Focus. Among 78 NFL tackles, Pears is ranked 72nd with a -16.3 overall rating. Among 34 NFL centers, Martin ranks 33rd with a -21.9 overall rating. And among 81 NFL guards, Devey ranks 77nd with a -13.1 overall rating.