Arguments on the Rookie of the Year seem to be favoring Robert Griffin III over Andrew Luck at this point in the season. Griffin's performance has been spectacular, certainly -- he's thrown for 2,660 yards and 17 touchdowns against just four interceptions. His 714 rushing yards on 105 carries translates to a league-leading 6.8 yards per carry, and his 6.5 AYPA is tied with Peyton Manning for third in the league.
Luck runs well, but nowhere near Griffin's standard -- he owns 216 yards on 44 rushes. Luck has thrown for over 900 more yards than Griffin and matched Grffin's 17 touchdowns. But his AYPA is a middling 5.1, 21st in the league and tied with Andy Dalton. Griffin has a 23-point EPA advantage and a 0.09 point per play advantage.
But for those who prefer to use more context-neutral stats -- as opposed to WPA, which has Luck second in the league at 4.32, over 1.5 wins better than Griffin -- there is one point in Luck's favor: the sheer volume of his output.
Washinton's' offense is obviously focused on Griffin, but the team uses the run liberally, rushing over 22 times per game (not counting Griffin's rushes). Alfred Morris carries the bulk of the load, with 1,106 yards (4.8 per carry) on the season. The Colts have rushed just 22 times per game themselves, but they've also run 117 more plays (just under 10 per game) more than Washington, and those extra plays are all directed through Luck and the passing game. All told, Luck has thrown 14 more passes per game than Griffin.
Basketball analysts have picked up on an essential point of the game: as usage rate -- the burden of the offense -- increases, efficiency tends to decrease. Steve Kerr was a more efficient scorer for the 1995 Chicago Bulls -- he shot 52.4 percent from three -- but there was no way he could take 22 shots per game with any efficiency. Jordan continued to excel even when confronted with the most difficult shots -- under duress, at the end of the shot clock, or both.
There's a similar relationship with quarterbacks. The idea that certain quarterbacks can only handle 20-to-25 throws per game with efficiency holds up in the data. Observe, the average yards per attempt given a certain attempt total (data includes all games since 2009):
The graph is smoothed out using three-attempt moving average (the R-Squared is from the raw data). With this smoothing, we can easily see the trend -- for roughly every 18 attempts per game, a quarterback tends to suffer about a half-yard efficiency drop.
However, this is only the typical efficiency progression with increased attempts. All quarterbacks will have at least a slightly different trend. Luck has been forced to throw over 50 passes on three different occasions and over 40 passes seven times. Griffin's top attempt total on the season is 39, although Griffin has ran roughly five times more per game than Luck.
Griffin, like most quarterbacks, had his biggest games on days in which he threw between 20 and 30 passes. Luck had some of his best games throwing over 35 passes and even over 45:
Griffin has lost a yard of efficiency roughly every six passes, whereas Luck has lost one just every 50. Both are a bit extreme, but both also are similar to other elite quarterbacks. Griffin's drop-off rate, for instance, is similar to those of Aaron Rodgers and Drew Brees, whereas Luck's is most similar to Brett Favre. You can try other quarterbacks (since 2009) by clicking here and checking the boxes on the right.
Luck's ability to keep his YPA above 6.5 as he goes over 50 passes is impressive. Only the league's best quarterbacks are typically allowed to sling the ball over 50 times per game. When we account for that survivor bias and look only at the middle 95 percent of games (from 23 attempts to 42 attemts), we find a one-yard efficiency drop for every 20 passes, not 37.
In that case, we'd expect a quarterback throwing 45 times per game to average 6.7 yards and one throwing 55 times per game to average 6.1 yards. Luck's high-pass games have ranged from 6.6 yards per attempt (55 attempts) to 9.0 yards per attempt (48 attempts). Griffin currently averages 8.2 yards per attempt on 27 passes per game. At 47 attempts, we should expect him to be at 7.2 yards per. At 50 and 55, the efficiency drops to 7.1 and 6.9 respectively. Luck has averaged 7.2 yards per attempt in his games over 45 attempts -- a touch better than we'd expect from Griffin so far.
The efficiency and raw productivity gap isn't completely closed through this lens -- quarterbacks throw roughly one extra interception per 33 passes, which only about halves the interception gap, something missed by YPA. YPA also doesn't capture Griffin's running ability. Accounting for the two-way threat and ball security Griffin provides, he would still be my current Rookie of the Year choice. Griffin has the ability to do enough with 20 to 30 passes to put a game out of reach, something only a few quarterbacks possess.
However, the race is closer than most efficiency metrics would suggest. Luck's ability to power the offense even with the burden of nearly 60 passes on his shoulders is tremendously valuable to his team, masking the poor running game. If Luck adds to his five game-winning drives and expands on his big WPA lead down the stretch, all while handling the bulk of the offense with even just slightly above-average efficiency, it could be an impressive enough performance to carry the argument at season's end.