Mike Zimmer deflected blame away from the Vikings offensive line after backup quarterback Case Keenum was pressured an NFL-high 51 percent of his pass plays on Sunday, according to Pro Football Focus.

So, what happened?

"It was a combination of things," Zimmer said Monday, adding: "Protecting and the quarterback depth, a lot of these things go hand-in-hand. [Keenum] got deep a couple times and we're not protecting at that depth. Some of it was that. We were late out of the snap one time. For the most part, we got on the right guys."

With starter Sam Bradford a game-time decision in Pittsburgh, the Vikings turned to Keenum for his first start since Week 10 last season. Some rust was evident. Keenum only took two sacks, but at least one could be pegged on the quarterback dropping too far back, which opened the field for Steelers defenders like Bud Dupree.

The Vikings allowed pressure due to a handful of gaffes. Zimmer pegged some of it on "communication issues." They also allowed the rare free run at Keenum when Steelers edge rusher T.J. Watt came unblocked. We'll get to that play shortly.

"We did have some communication issues," Zimmer said. "There was a couple times we were late off the ball. It wasn't just on [Keenum], it was a combination of things."

Let's take a look at four examples of the Steelers' pressure, a critical element to the Vikings' failure on offense in Pittsburgh. Here to help is Dan Hatman, a former NFL scout and Director of Scouting Development at The Scouting Academy. You can follow Dan on Twitter at @Dan_Hatman.

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On this third down, the Steelers blitz to stress the right side. Cornerback Joe Haden (21, far left) is set to come off the edge. Bud Dupree (48, middle) takes a wide rush, which is where Keenum eventually helps this blitz get home by escaping backward instead of stepping up — leading to one of six Ryan Quigley punts.

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"Looks like Keenum sets up at 6-7 yards in the gun, then retreats to almost 12 yards in his drop," Hatman said. "There are almost no OTs in the NFL I would trust to carry Dupree's speed to that depth. The rest of the 6-man protection does a good job versus the nickel blitz and would have held up well. Finally, [Cameron] Hayward was too much for [Riley] Reiff here, collapsing the pocket."

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When the Vikings set up 'manageable' third downs, let's call them third-and-6 or shorter, they were effective. Minnesota converted 4 of 5 third downs in those situations, except for this one below. On the surface, the untrained eye could blame Keenum not getting the ball out in time, but the pressure from left guard Nick Easton's lane helped stall this drive, according to Hatman. Keenum's progression eventually brought him to the open Kyle Rudolph, though he was hit when he threw. The failed fake punt attempt came after this play.

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"Right side of the OL handles [tackle/end] twist game," Hatman said. "Berger carries the penetrator as the protection calls for Elflein to be pushing that way and he picks up the outside linebacker. The direct pressure came from the DT softening Easton's outside shoulder with the bull rush. In addition, that pressure came on the same side as the primary read, so with the throwing window taken away, Keenum came back across the formation and even though Rudolph was open, the pressure was already home."

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On this third-and-10, the Steelers again bring a blitz (24 times total, per Zimmer). The pressure comes off right tackle, but running back Dalvin Cook appears responsible for defensive back Mike Hilton in this protection scheme. Hilton gets one of the Steelers' seven hits on Keenum, who doesn't help his blockers by escaping backward again.

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"You can draw up 6-man protections in many ways, but it looks like [Dalvin] Cook is scanning inside-out. With [Mike] Remmers blocking down versus the defensive end, Cook would have to come across and pick up the edge blitzer. Many protections like to work inside-out to keep immediate pressure off the QB as edge pressure takes longer to get there. As such, I'd be inclined to think Remmers was doing his job and Cook didn't find the rusher in time to make proper contact. Tough block for him."

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The Vikings' best drive of the first half was stalled, in part, because of three straight plays with Steelers pressure on Keenum. Right after Keenum's 24-yard pass to receiver Adam Thielen, the Vikings allow Watt a free run at the quarterback. The Steelers overloaded left tackle with Watt's wide alignment and a linebacker (#98) blitz, which Reiff attempted to pick up. This one broke down at multiple spots. Zimmer alluded to the play Monday, noting the line was sliding away from the blitz.

After the play-action handoff, Cook had little chance seeing three Steelers defenders between Watt, the linebacker and defensive tackle pressure between Elflein and Easton.

"Sometimes if you got everybody out and about and they bring an extra guy, and the [offensive] line is sliding away, they're going to have a free runner," Zimmer said. "The [blocker] has to come back in and take the most dangerous guy. Sometimes that happens."

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"Again, with this 6-man protection, Reiff and Cook need to pick up 90 [Watt] and 98 [Vince Williams]," Hatman said. "There is some miscommunication there as Reiff either did not see 90 or thought he had Cook protecting that edge."