Some thoughts on YAC/the deep ball/separation/pass protection and how it all ties together for #49ers/QB Brock Purdy through four games:
-- Yes, Niners YAC numbers are way down (3.4 yards/completion is tied for last in NFL). Some of that is because of the varied absences of McCaffrey, Deebo and Kittle.
-- That has been offset in part because Brock Purdy is pushing the ball down the field more. Purdy's at 10.4 air yards/attempt which is 2nd highest in NFL (Anthony Richardson first at 12.0). And 15.6% of his attempts have been 20+ air yards, which is tied for 4th highest.
-- The average separation on his passes (this is just for players who are being targeted on throws, not if open elsewhere and not targeted) is 2.78 yards, which is lowest in the NFL. His 24.6% tight window attempt rate is second highest among passers with at least 10 attempts. Less separation at time of catch naturally makes YAC more difficult.
-- How does it tie into pass protection? Well, Niners are allowing a 31.3% pressure rate which is 21st in the NFL. But it's worth noting that Purdy also has the longest average time to throw in the NFL at 3.14 seconds. The league average, for what it's worth, is 2.79 seconds. Purdy is being pressured on 33.3% of drop backs when it takes 3 seconds or more to throw. When it's below 3 seconds, that number drops to 21.3%. That is still VERY high, so this isn't to say the pass protection has been great or even good for the most part. And Purdy obviously is able to extend plays with his scrambling ability which factors into all of this as well.
-- The point here is just that the cost of doing business deep down the field is going to create additional pressures, even when teams only rush three. Protection can be good but when you get beyond the normal amount of time to protect, naturally pressures are going to increase with longer developing route combos/throws. Likewise, YAC is going to drop a bit when teams are dropping so many into coverage and leaving less space for pass catchers to run free over the middle of the field.
-- If anything, Purdy's performance as teams seem to be adapting to what the Niners have done well offensively and also without McCaffrey available should be an encouraging sign for his adaptability as his career moves forward. SF must improve in the red zone and pass pro needs to get better, to be sure. But this offense is still 6th in offensive EPA and 5th in efficiency. With defense and special teams as is, there's room for improvement and it might be necessary if this is a team that's going to have to win more shootouts as the year rolls on.