"It was him with a number of other guys," Shanahan told reporters this week, "guys I was hoping were going to come out earlier, but they didn't. And so we looked at guys more that year, and (the) next year we had Jimmy (Garoppolo)."
Allen is 6-foot-5 and close to 240 pounds, making him close to Cam Newton-sized. That can make bringing down the quarterback a challenge.
"He's as good as advertised," Shanahan said Friday morning on KNBR's Murph & Mac show. "The skillset that he has, with his mentality, you don't see many guys that big, who can run that fast, who also have the mentality to run people over. So, if you sit there and think he's going to go down easy, you're going to get extremely embarrassed because he can run you over.
"You better bring it on him, and if he decides to slide, that's the hardest thing about it because to have the mentality to not get trucked by basically a truck coming at you, you've got to bring it and match it. And if they go down at the last second, you've got to do everything you can to not touch the guy. It's a very fine line with that. But if you go in there with any hesitation against a guy with that size and that speed, you're in trouble."
49ers defensive lineman Kerry Hyder knows the challenge of facing a big quarterback like Allen, who can also be mobile if needed. Still, you can't hesitate, or you risk giving up a big play anyway.
"You can't slow down," Hyder told KNBR's Greg Papa and Mark Willard. "In this league, you'll miss a tackle, or he'll break a tackle. You've just got to go fast, and if he slides, do your best to stay out of the way."
Allen is having his best NFL season. The Bills' third-year quarterback has completed 68.8 percent of his passes for 3,028 yards with 22 touchdowns and eight interceptions. Buffalo is 8-3 and sitting atop the AFC East.
"Also, our D-line knows, and our whole defense knows, just the D-line can't take care of him," Shanahan continued. "It has to do with a lot of people. It has to do with all 11 guys out there, and that's why people are talking about this guy the way he is. Hopefully, we can frustrate him a little bit, make it hard on him, and make this a good game."
You can listen to the entire conversation with Shanahan below.
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