The San Francisco 49ers have been on a roll, winning twelve straight games. And as BetOnline customers know by now, they have gone seven of those games with a rookie starting at quarterback. Not only that, he's a seventh-round draft pick who was the final selection. So this is like a fairy tale.

But will the clock strike twelve on Brock Purdy? He has held steady against both Seattle and Dallas in the playoffs, but sooner or later a rookie signal-caller has a blowup.

Doesn't he?

We'll see, as the Niners face off against the Philadelphia Eagles with a trip to Super Bowl 57 on the line. It is set for 3 PM ET at Lincoln Financial Field, to be televised by FOX.

For this discussion, we're not going to talk about whether Purdy can steer his team to SB 57, but whether he can topple a certain total on his passing yardage. Here are the numbers as you'll find them at Prop Builder:

Brock Purdy - Passing Yards

Over 221.5 Yards +100
Under 221.5 Yards -130

Purdy went 19 for 29 for 214 yards against Dallas last week, and that was the best defensive unit he has faced to date. The Eagles aim to be effective in a different way, as they will bring as much heat as they possibly can. These guys rang up 75 sacks this season, which is an absurdly high total. And they ranked #1 in the NFL this season, in terms of both passing yards allowed per game and per pass (5.4). With a secondary of corners James Bradberry and Darius Slay and safety CJ Gardner-Johnson (tied for NFL lead in interceptions) patrolling, Purdy won't likely get a lot of chuck plays, which probably dictates he'll go underneath and hope that his receivers can do something with the ball once they catch it.

And then, of course, there's the run game. Over the past three games, the Niners have run the ball 54.3% of the time, and with Elijah Mitchell having returned to the lineup to join Christian McCaffrey, they don't have any worries about continuing that trend, especially as the Eagles are not all that stout against the run. Philadelphia gives up 4.7 yards per rushing attempt, although they have done their best to beef up the middle with the likes of Ndamukong Suh and Linval Joseph.

Veteran Trent Williams, who is ticketed for the Hall of Fame, carried the #1 offensive tackle grade this season from Pro Football Focus, and he was also #1 specifically for run blocking.

One of the things the 49ers like about Purdy is that he protects the ball very well. He has now thrown the ball 229 times and suffered only four interceptions, and that includes no picks at all over his last three games.

Whether that factor really impact us here is something we're not all that sure about, except that the philosophy might be "safety first," as long as the Eagles haven't gone off to a sizable lead.

When examining how far Purdy actually throws the ball, what needs to be considered is that his Intended Air Yards per attempt is just 6.6, which would put him down near the bottom of the list of NFL starting quarterbacks. However, he's also getting an average of 6.2 yards after the catch from his receivers, which, projected over a full season, would put him below only Patrick Mahomes and his own teammate, Jimmy Garoppolo.

So the Eagles' success is going to be predicated not only on making him hurry into bad decisions, but also keeping everything in front of them and not letting Deebo Samuel, Christian McCaffrey, George Kittle et al to go wild.

Our best guess is that of Purdy wants to play the role of the hero, the Eagles are going to make him earn it, all the way down the field. And that leads us in the direction of an "under" on this prop.

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