Data scientist, physicist, and fantasy football champion

Effect of starting/backup QB on DEF fantasy points

Aaron Rodgers is out for the season, Jameis Winston might be out this week, and Mariota may sit as well. Conventional wisdon says you start a defense against the backup QBs, but exctly how much better do fantasy defenses do against backup QBs? Is it worth it to stream a defense based on the QB that’s in? What if it’s an otherwise bad matchup? What is a backup QB worth?

I determined whether a QB was a starter or backup for a given year based on how many games they played that year. If they played more than 5 games in 2015 or 2016 then they were a QB1 and if they played more than 8 games in 2017 they were the QB1, otherwise I called them QB2. This actually gave me really good results and I didn’t find anyone that I would have called a “starter” in the QB2 category except for guys at the end of their careers or guys who took a big injury early in the season and were out for more than half of the season. I had initially tried to break it up based on mean fpts per game, but there were a few starters who score poorly and a few backups with 1 or 2 games who did very well. This obviously isn’t perfect, but I think the way I broke this up was reasonable. If you disagree or want to see something else, yell at me on Twitter (@FFDataStream).

This system gave me 30 starters in 2015, 31 in 2016 and 33 so far in 2017. It also gave me 48 backups in 2015, 40 in 2016, and 15 in 2017. That number of starters in the low 30s seems very reasonable to me.

Let’s see how QB fantasy points are distributed by starter/backup:

.QB score by rank-1.png

This makes sense to me. Starters do better, backups are sometimes brought in for parts of a game and not asked to do much, so they’ll likely have very few points. Obviously you shouldn’t be starting these guys, but why are they worse? Are they getting sacked more?

.QB sacks by rank-1.png

Maybe, but not much. That tail has a low density, but there are some backup QBs getting sacked more than 6 times a game. But it’s not too surprising that it’s still peaked around 2; some of these guys are only in for a quarter. Getting sacked twice in that time is bad, but it won’t show up in a plot like this. Sacks aren’t prorated.

What about interceptions?

.QB interceptions by rank-1.png

It looks like backups are getting sacked less, but again, they’re often only in for a little while and aren’t asked to throw as much.

Let’s take a look at fantasy defense (DEF) scores when there’s a starter in or a backup in. Here’s another decision I had to make: when a fantasy defense got 8 points in a game, how do you determine whether it was against a QB1 or QB2? If a QB comes out in the first quarter I’d probably consider it the QB2’s game, whereas if they come out in the 4th quarter it’s the QB1’s game. If the QB1 just sat at the end of the game to avoid injury and catch his breath how do you count the points?

I tried 3 methods, but I’ll only show you the last one.

  • Method 1: I split it up by whether the QB1 was ever in the game
  • Method 2: I split it up by whether the QB2 was ever in the game
  • Method 3: there are 3 types of games: games where only the QB1 ever played, games where only the QB2 played, and games when they were both in at least a little.

They give very similar results. Again, if you’re crazy I’ll show them all to you. Otherwise, just trust me and take a look at the following:

.DEF score with QB1 andor QB2 in-1.png

Yeah, that’s what I’m looking for. That’s a nice, clear shift in score based on whether the starter or backup was in. In games where ONLY the starter played, Fantasy defenses scored a little less than in games when only the backup played. How much less you ask? It’s about 2.34 points.

So there you have it. If a backup QB is playing you can expect 2.34 more points from your fantasy defense. That’s nothing to sneeze at and something to consider this weekend when streaming defenses. If you suspect that your defense will score at least 2.5 more points than the one going up against the backup, then there’s no need to switch.

Just something else to thing about. As always, good luck to everyone out there not in my league.

Effect of starting/backup QB on WR fantasy scores

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