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.