Why did the Bears drop pass-rush stud Khalil Mack into coverage so often Sunday?

The day after the Bears traded a bounty — then paid another one in salary — for outside linebacker Khalil Mack, coach Matt Nagy explained why he was so crucial against the NFL’s best passers.

‘‘You know, he gets to the quarterback every play,’’ Nagy said then.

Against arguably the greatest quarterback of all time, however, the Bears insisted on playing a scheme Sunday that kept Mack away from Patriots star Tom Brady.

Mack rushed the quarterback only 14 times — seven times in each half — in the Bears’ 38-31 loss, playing in coverage the rest of the time the Patriots passed. He lined up over the left tackle after mostly playing on the opposite side all season. His only tackle came in pass coverage.

It was part of defensive coordinator Vic Fangio’s strategy to rush (mostly) only three down linemen. Fellow outside linebacker Leonard Floyd played more in coverage than he had all season, too.

What role did Mack’s injured right ankle play in the decision? Was chasing slippery pass-catchers really easier on his ankle, which he hurt the week before, than running straight ahead toward the quarterback?

Fangio, who has control over the Bears’ defensive strategy, won’t meet with the media until Thursday, and Mack left the locker room Sunday without speaking with reporters.

So it was left to the offensive-minded Nagy to explain the intersection of strategy and injury Monday.

‘‘It creates another defender for the quarterback to have to throw around,’’ he said, ‘‘especially when you know or think or predict that they’re not going to run the ball. If you think they’re going to run the ball, that’s different because now only three guys are rushing.

‘‘It creates another element to have [Brady] throw around. And don’t think that’s the first time he’s seen that. He’s seen that defense a lot from a lot of different teams.

‘‘When you decide to drop eight against him, you have to be good at it.’’

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The Bears were not. Brady’s 108.2 passer rating was his second-highest in his last 12 regular-season games, and his three touchdown passes tied a season high.

Nagy conceded that Mack, who often rushed with his hand in the dirt as a member of the Raiders, likely would have done the same if his ankle had been healthier.

Mack played 84 percent of the Bears’ defensive snaps. While his mere presence drew double-teams when he did rush, it’s fair to wonder whether the Bears left a better pure coverage option on the bench.

The decision to drop eight players into coverage came at the expense of inside linebacker Roquan Smith, who played only 55 percent of the Bears’ defensive snaps. He had the team’s only sack — on a blitz.

Playing Mack as much as the Bears did — regardless of how he was deployed — required trust, Nagy said.

‘‘The player has to understand where we’re coming from as a team as to where you’re at percentage-wise,’’ he said. ‘‘We all know that he’s not 100 percent, but where are you at?

‘‘That’s where we trust him, he trusts us and then we go ahead with the action plan. And that’s what we ended up doing. It’s not an easy decision or process.’’

The Bears will continue to monitor Mack, who was held out of two practices last week and was limited in the third. There’s a chance, Nagy admitted, that it might be awhile before Mack is himself again.

‘‘Every player is a little bit different,’’ Nagy said. ‘‘He’s kind of a freak in regards to his health and how he goes and pain tolerance. So we’ll have to just keep a real clean eye on it.’’

The good news was that the game didn’t exacerbate Mack’s injury, Nagy said.

‘‘It was probably similar as far as the pain,’’ he said. ‘‘I don’t think it was any better or any worse.’’