Tim Tebow is breaking the game probability model. How can a quarterback lead his team to victory while going 2 for 8, for 69 total passing yards? It’s widely accepted that passing efficiency is the main driver of team success, but what if an astounding 8.6 yards per attempt comes on only two completions?
Tebow is 3-1 as a starter this season. So how is he doing it? Is it with his arm, his called runs, or his scrambles? It’s none of the above. It’s with defense and special teams.
At my Web site, I rely on two statistics to parse apart each player’s contribution to game outcomes. Win Probability Added (WPA) measures how much a player’s direct participation changed his team’s chances of winning the game. Expected Points Added (EPA) measures a player’s impact on the net score difference. One of the advantages of stats like WPA and EPA is that they are agnostic as to whether a play was a pass or run, or any other type of play. This allows us to measure the total contribution of a player in a single number.
Tebow is decidedly negative in both of those stats for the full season (-0.35 WPA and -13.3 EPA), but fortunately for the Broncos, the vast majority of the damage was confined to a single game: his second start in a game against the Lions. A closer look at his numbers indicates he has performed modestly well in his other three starts.
Against Miami, Tebow performed poorly until the last few minutes of regulation, when he rallied the Broncos to tie the game. His last-minute heroics may have been thrilling, but they were needed only because of the hole he had put his team in to that point. The game was ultimately won thanks to a Dolphins fumble and a 52-yard Matt Prater field goal.
The thriller against Oakland unfolded in much the same way. Carson Palmer threw three interceptions. Running back Willis McGahee tied the game with a 60-yard touchdown run at the end of the third quarter and totaled 0.30 WPA and 4.6 EPA. The Broncos took the lead for good on an Eddie Royal 80-yard punt return for a touchdown. Tebow played fairly well in his own right. He totaled 4.6 EPA and -0.03 WPA, threw no interceptions and gave up only two sacks.
Last Sunday’s victory over the Chiefs was mostly a defensive victory. Matt Cassel was held to 2.4 yards per attempt and was sacked four times. The Broncos’ defense held the Chiefs to 10 points, 7 really if we don’t count a pointless field goal in the final seconds. Tebow made a big impact in this game, as one of his two completions was a 56-yard touchdown pass.
In the three victories, Tebow totaled 0.03 WPA and 9.3 EPA, both of which are slightly above average. In other words, he helped more than hurt his team, but only barely. The Broncos’ running game, excluding Tebow, totaled 1.67 WPA and -0.1 EPA in those same games. (When the WPA and EPA are largely split like this, it indicates over-performance in game-changing clutch situations.) The Broncos’ defense was responsible for 0.72 WPA and 11.5 EPA in the three wins.
I suspect Tim Tebow’s outing tonight against the Jets’ defense will resemble his struggle against the Lions more than his three wins as a starter. Here are the game probabilities for Week 11. (For more on the prediction model and its accuracy, see this post.)
Brian Burke, a former Navy pilot who has taken up the less dangerous hobby of N.F.L. statistical analysis, operates Advanced NFL Stats, a blog about football, math and human behavior.
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