Before the start of the 2014 NFL season I wrote this preview
which highlighted the factors that are most strongly correlated with winning.
Turnover differential, the amount of times you take the ball
away from your opponent, compared to how frequently you gift the ball to them
by interception or fumble, is unsurprisingly strongly correlated with game
result.
Possessions are roughly equal numerically during a game. So
if you end an opponent’s drive by a turnover, you inevitably deprive them of
potential points, while often increasing your own scoring potential from your
subsequent drive because of good field position.
A side having a turnover differential of +2 in a match will
see that team winning over 80% of such games. Any higher and the win percentage
rises to 90%+.
Therefore, the importance of turnover differential is both
huge and widely recognised. Former Ravens coach Brian Billick writing for NFL.com
uses turnover differential as a major component of a statistic he calls “toxic
differential” which also charts big plays, in excess of 20 yards allowed and gained.
Billick describes this combined statistic as controllable, which
implies that a team that has done well in such categories as turnover
differential in the past will continue to do well in the future and in doing so
will reap the expected positive results.
However, if we look at season to season correlation between
turnover differential for teams, there appears to be virtually no persistence.
That is not to say that there is no talent associated with
turnovers. For instance an experienced NFL quarterback may be consistently less
prone to turning the ball over than a rookie and some side may encourage a gambling
cornerback to go for interceptions. But there is also likely to be a large
degree of luck and randomness involved in turnovers.
This is perhaps most visible when sides are attempting to recover
or secure a fumble. The ball can pass through numerous hands before it is
finally claimed.
In 2013, seven sides had a turnover margin of +10 or more
averaging a turnover differential of +14 and their combined winning record was
0.65. This season, the same seven teams are on course to average a turnover
differential of -1 over a 16 game regular season and their current combined
win% has fallen to 0.53.
At the other end of the scale the five sides that had
turnover differentials of -10 or worse have improved their average differential
from -15 to a projected -5 and their winning % from 0.36 to a current 0.42.
So a big driver of game outcome, turnover differential is
likely to be partly a product of luck, especially at the extremes and a side
that has benefitted from extreme splits may not be as fortunate in the future.
The team with the best current record in the NFL is Arizona.
Their 7-1 record in one of the NFC’s toughest divisions the NFC West has been
achieved with a +9 turnover differential compared to their -1 in 2013.
The Cardinals may have worked to improve their turnover
differential. The narrative from within the dressing room is understandably one
of renewed confidence and positivity. And Billick, who has won more Super Bowl
than most people on the planet, may be correct in that turnovers are largely
controllable. But consistently, turnovers do appear to be at least partly due
to luck for the majority of teams.
Arizona may not be quite as worthy of their current 7-1
record. Pythagorean estimates, which chart points scored and conceded and
partly account for the perceived luck that exists where teams win lots of close
matches, has the Cardinals as a 5-3 team.
The NFL season is of course geared towards the Super Bowl
and Arizona are currently fifth favourites trailing behind division rivals Seattle,
who currently trail the Cardinals by two games. So there is an acceptance, even
within their own division that Arizona are perhaps not the 7-1 team that they
appear, especially if their turnover differential returns to more normal levels.
However, this may not matter to Arizona, even in the post
season against quality opponents. If they play 0.5 football for the remainder
of the season, their 11-5 record should get them into the playoffs and if they
play to their Pythagorean estimates, a 12-4 could land them a top two seeding.
The turnover record of seeded teams and the implication that
turnover differential is a transient quality, appears to highlight the amount
of influence random chance has on deciding the destination of the Super Bowl.
Over the last ten seasons, number one seeded sides had an
average regular season turnover differential of +13.5, number two seeds, 11. The
figure was 8 for number three seeds and around 5 for 4th, 5th
and 6th seeds. Playoff teams need to be good, but top seeds need to
be good and perhaps also lucky.
Average Turnover Differential For Seeded Teams Since 2003.
Average Turnover Differential For Seeded Teams Since 2003.
| Post Season Seeding. | Average Turnover Differential. |
| 1 | 13.5 |
| 2 | 11.0 |
| 3 | 8.3 |
| 4 | 5.1 |
| 5 | 5.5 |
| 6 | 5.4 |
So turnovers and possibly, by implication, luck played a
role in gaining a team a high seeding. And that seeding comes with huge
benefits. A top seeded team has two guaranteed home field games to reach the
Super Bowl, while a 6th seed needs to negotiate three road games to
reach the same destination.
If we assume (probably unrealistically) that the difference
between 1st seed and 6th seed has come about purely by
chance, the rewards of the playoff schedule will see the number one seed
attempting to overcome odds of 5.0 to lift the trophy, compared to a road weary 25.0 for the
similarly talented sixth seed.
So Arizona may have been fortunate so far. But they have
already banked a 7-1 record and a tangible, if perhaps undeserved reward awaits
their lucky run if they can use their present record to secure a top seed.
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