Bengals vs. 49ers NFL Week 8 odds, trends: Spread, total drop with Brock Purdy in concussion protocol; Sam Darnold on track to start

Arguably the marquee matchup in NFL in Week 8 is Cincinnati at San Francisco in a possible Super Bowl 58 preview. Both teams lost their respective conference championship games last season. The Bengals, healthy out of their bye, opened as 5.5-point underdogs on the SportsLine consensus but are now -3.5 with the news that 49ers quarterback Brock Purdy is in the concussion protocol and may have to miss the game. Sam Darnold would start in his place. The total is down from 46 to 45.

Purdy was not visibly injured in Monday night's 22-17 loss to the Minnesota Vikings, but San Francisco coach Kyle Shanahan said Wednesday that Purdy entered the protocol after he started showing symptoms on the flight home from Minneapolis. It was also the first game of Purdy's NFL career in which he threw two picks.

Purdy simply has not looked the same in back-to-back weeks. Both star receiver Deebo Samuel and All-Pro left tackle Trent Williams are on the shelf, meaning Purdy is without both his top target and his primary protector. Samuel will be out again this week and Williams is doubtful. Purdy has been blitzed on 42.8% of his dropbacks this season, the highest rate in the NFL. He is second in the NFL in overall passer rating (107.2) and second in yards per attempt (8.6), trailing Miami's Tua Tagovailoa in both.

Looking at other players who landed in the protocol this season, it's very unlikely Purdy clears in time for Sunday, especially given that he has one fewer day to recover because his team played Monday. The NFL is being much stricter on its concussion protocol this year.  

Darnold signed a one-year free-agent deal in March and won the backup job over former No. 3 overall pick Trey Lance, with Lance then traded to Dallas on the eve of the season. In 2022 with the Panthers, Darnold started six games and completed 58.6% of his passes for 1,143 yards, seven touchdowns and a passer rating of 92.6 to go along with 26 rushes for 106 yards and two touchdowns. 

He is now 21-34 as a starter in his NFL career. Among 26 active QBs with at least 50 career starts, Darnold ranks last in completion percentage (60.0), TD:INT ratio (61:55) and passer rating (78.2). Brandon Allen is the only other QB on the roster. The 49ers are 9-29 with starting QBs other than Jimmy Garoppolo or Purdy under Shanahan, compared to 48-19 with Garoppolo or Purdy. 

San Francisco is 8-0 against the spread in its past eight home games, tied for the ninth-longest such streak in the league since 1970. Cincinnati is 7-0 straight up and ATS in its past seven regular-season games vs. NFC opponents.

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