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Against the Saints in week four, Jay Cutler completed 20 of 28 passes for 164 yards, which translates to a sparkling 71.4% completion percentage. But that was about as misleading as it gets. Cutler also was sacked four times — a 12.5% sack rate — and several of those completions were pretty meaningless. In fact, Cutler threw just 7 first downs against New Orleans.

When you hear the 71.4% completion rate, you think: pretty good. You’d be wrong. Completion percentage ignores sacks (it shouldn’t), and it treats a completed pass for a first down the same as a completed pass for zero yards. On 32 dropbacks, Cutler threw just 7 first downs — a 21.9% rate that is more meaningful than his completion percentage. Why is it more meaningful? Well, the Dolphins were shutout against the Saints.

Want another example? Against the Redskins in week 3, Derek Carr completed 19 of 31 passes, for a nominally effective 61% completion rate. But Carr was also sacked four times (which, again, should be in the denominator when looking at completion percentage) and picked up just three first downs. Three! So while he completed 61% of his passes, Carr threw for a first down on only 9% of his pass plays against Washington.

How about from this weekend? In his first start of the year, Titans quarterback Matt Cassel completed 66% of his passes and produced a passer rating of 85.5 against Miami. That’s pretty good, right? Well, it isn’t when you have drives that like this that increase your completion percentage and passer rating:

Cassel was sacked six times on the day and threw for just 9 first downs. So while he was 21/32 on the stat sheet, he was also 9/38 at throwing for first downs, a very poor 24% rate. The Titans had 14 drives, and one of them was a 4-play drive for -3 yards that resulted in a field goal because it started at the Dolphins 24; the other 13 drives produced one touchdown, two fumbles, and ten punts. Tennessee lost, 16-10, despite Cassel completing 66% of his passes: or, maybe they lost because Cassel completed 66% of his passes playing that style.

A high completion percentage shouldn’t be any offense’s goal; instead, it feels like more and more quarterbacks (and offensive coordinators) are treating it like the ends and not the means.

The graph below shows completion percentage in the NFL (excluding the AFL) from 1950 through five weeks of 2017. That line is in blue and plotted against the Left Y-Axis; as you can see, it’s been increasing steadily over the last seven decades.  Plotted in orange and against the Right Y-Axis is the percentage of pass plays that have gone for first downs.  That’s also increasing, although it’s been a little bit bumpier.

In the late ’50s and early ’60s, the ration between completion percentage and first down percentage (of all pass plays) was around 60%; right now, that ratio is nearly down to 50%, and that’s despite sack rates being a bit lower now, too. Still, the real meat on the bone to this data is on the team-by-team level, not league-average data. More on that later in the week.

  • Adam

    First downs are always a successful play (from an EPA standpoint), while completions are often unsuccessful. This is the primary reason why 1D% is a far better measure of QB play than C%.

    • David

      I disagree – 1D% is a better measure of offensive play than C%, but as long as the offense is getting first downs, it doesn’t matter if they come through passing, or running.

      Moving the ball forwards is always better than not. Therefore, completion percentage (as long as we’re assuming not a lot of backwards passes) is a good measure. Whether a given play which attains forward movement gains a first down is subject to a lot more than the passer – there are random elements, and more significantly playcalling aspects to consider.

  • Adam

    The idiocy of passer rating has exacerbated the prevalence of worthless completions. I bet most QB’s realize they can pad their rating by throwing checkdowns and taking bad sacks instead of throwing the ball away. I remember reading that a few QB’s have incentive clauses in their contract based on reaching a certain threshold in passer rating. No wonder they take the easy completions!

    As you mentioned in a previous article, Colin Kaepernick’s 2016 was the most blatant manipulation of passer rating that we’ve ever seen. And he played that way to elevate his perception among GM’s, and NOT because it helped his team win.

  • Richie

    I think part of the reason completion percentage has gone up is because of Bill Walsh’s concept that a short passing play is as good as a run.

    Is it true? Part of the value of the run is to keep defenses honest, to open up the passing game. Maybe the 4-yard, low-risk pass play has nearly the same expected gain as a running play. But does it remove the part about keeping a defense honest?

    I am curious to see the team-by-team data. Do teams that run the ball more end up with a more efficient (by first downs) passing game?

  • AgronomyBrad

    Somebody wanna forward this article to Peter King?

    • Josh Sanford

      If so, make it mass emailing to almost ALL of the talking heads.

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