Fantasy Football Week 18 Start ‘Em, Sit ‘Em: Brock Purdy vs. Baker Mayfield

Evaluating who to play in fantasy football between San Francisco 49ers QB Brock Purdy and Tampa Bay Buccaneers QB Baker Mayfield.

Dec 28, 2025; Santa Clara, California, USA; San Francisco 49ers quarterback Brock Purdy (13) celebrates after scoring a touchdown against the Chicago Bears in the first half at Levi's Stadium. | Kyle Terada-Imagn Images

Two QBs who are coming off putting up insane fantasy numbers in week 17, Baker Mayfield and Brock Purdy, will both be in action early this week, playing on Saturday. Here is a breakdown on who to start and who to sit between Purdy and Mayfield this week in fantasy football.

Brock Purdy

Dec 28, 2025; Santa Clara, California, USA; San Francisco 49ers quarterback Brock Purdy (13) throws a pass against the Chicago Bears in the first half at Levi's Stadium. | Sergio Estrada-Imagn Images

Coming off a week 16 game where Brock Purdy put up the most fantasy points with a five-TD passing game, he hardly slowed down in his play in week 17 against the Chicago Bears. In the game against Chicago, Purdy went 24-33 passing for 303 yards, threw three TDs, and one interception. In fantasy football, in week 17, it gave Purdy the QB1 spot once again. He will look to continue this play to close out the regular season against the Seattle Seahawks.

The Seahawks this season are allowing the 12th fewest passing yards per game. In their last three contest, they have allowed a TD-to-INT ratio of 4-2. They are coming off an uberly impressive outing in week 17 against the Carolina Panthers, where they held QB Bryce Young to just 54 passing yards. 

Purdy, despite missing some time this season due to injury, did play against the Seahawks earlier this season. All the way back in week 1 against Seattle, he threw for 277 yards, two TDs, and two INTs against them.

Baker Mayfield

Dec 28, 2025; Miami Gardens, Florida, USA; Tampa Bay Buccaneers quarterback Baker Mayfield (6) throws downfield during the second quarter against the Miami Dolphins at Hard Rock Stadium. | Nathan Ray Seebeck-Imagn Images

After struggling mightily in the past weeks, Buccaneers QB Baker Mayfield finally produced a good fantasy performance. Before week 17, Mayfield, in three of his last four games, threw for under 200 passing yards and had less than two passing TDs. Against the Miami Dolphins on Sunday, Mayfield had 346 passing yards, two TDs, and two INTs. This ranked him as QB12 for the week in fantasy football.

Stacking another solid outing against the Carolina Panthers on Saturday will be difficult for Mayfield. In their last three games, they are allowing the seventh fewest passing yards per game in the NFL. One of these games was against the Buccaneers, where Mayfield threw for 145 yards, one TD, and one INT against them. Mayfield was one of the two QBs who threw for under 200 yards against the Panthers in these contests. Also, Mayfield and the other two QBs in this stretch combined for a TD-to-INT ratio of 3-2. The last QB to throw for three or more TD passes against them was Dallas Cowboys QB Dak Prescott in week six.

Final Verdict

When it comes to who should start and who should sit between Purdy and Mayfield, Purdy should start, and Mayfield should sit. Purdy, in his last two games, has been arguably the best QB in the NFL, and undoubtedly the best QB in fantasy football. With this, combined with the fact that he was solid against his week 18 opponent earlier this year, he is the obvious start. Mayfield did have an encouraging game in week 17, but his down game against the Panthers in week 16 also plays a part in giving Purdy the start in this debate.