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Footy Forensics: What do the stats say about the Tigers and Crows?

The Crows are strong in most areas, but will it be enough to overcome the Tigers' home-ground advantage?

After one of the most evenly balanced seasons in league history, more even than any other major sporting league, the 2017 finals series has been a bit of a fizzer so far. Bar the extra-time antics in Adelaide between the Power and Eagles, and the first two-and-a-half quarters of the Tigers-Giants preliminary final, the finals have largely failed to deliver on the promise of the regular season. But this weekend promises to be different.

The Crows are the narrow favourites heading into the grand final, with the betting market odds implying that they have a 56 percent chance of taking home the flag. That's close enough to a toss up to give the Tiger army real hope. Our Elo model should give them even more hope; it's tipping a narrow Tiger win, helped along by home-ground advantage.

What does Elo think?

The Crows have spent almost the whole season as the highest-rated team in the competition, and that's where they sit after the preliminary finals. The Elo ratings think the Tigers are the third best team in the competition, just a nose behind the ignominiously-eliminated Swans. The gap between the Tigers and the Swans is tiny, and the gap between the Tigers and Crows isn't much bigger.

DATA: ELO RATINGS BASED ON DATA FROM AFLTABLES.COM

Both sides are firmly above the 1600 mark that usually indicates a real premiership threat. If we compare the two contenders to past premiers in the AFL era, the Crows' Elo rating is right in the middle of the pack - a very strong 1668. The Tigers' 1640 rating is also premiership-worthy, a tick above last year's Bulldogs and a number of other past winners.

DATA: ELO RATINGS BASED ON DATA FROM AFLTABLES.COM

Using the Elo ratings, we can tip the winner of the grand final. You'd think that with the Crows rated the higher team, they'd be the favourites to win, but it's not that straightforward. The Elo system also gives teams a home-ground advantage, based on how many games each side has played at the ground in the past three seasons, and how far each team has had to travel to the game. Once this home advantage is factored in, Elo thinks the Tigers are narrow, six-point favourites to win the flag, with a 56 percent chance of victory. Without the disadvantage of playing at the MCG, the Crows would be slim three-point favourites to win.

Attack and defence

Elo is a handy, and powerful, way to summarise a team's quality in a single number, but of course there's a bit more to footy than that.

We're often told that to be 'premiership standard', a team has to average at least 100 points per game, while conceding fewer than 86 points per game. Using that somewhat arbitrary measure, Adelaide clearly has a premiership-standard attack, averaging 109.8 points per game, and a fairly stingy defence that gives up an average of just 79.1. The Tigers are out of the zone - their defence is more than tight enough (average 74.6 points conceded per game), but their attack isn't up to standard. But neither were last year's Bulldogs, who had an even lower average score than this year's Tigers. Richmond's profile looks similar to the reigning Dogs and the 2005 Swans - it's not impossible to win it all when averaging only 90 points per game.

DATA: AFLTABLES.COM

One problem with comparing today's contenders to the past champs based on how much they've scored and conceded is that the game has changed. Back in the early 90s, the average score was over 100 points per game; nowadays it's less than 90. So to properly compare, the Tigers and the Crows to the attacking records of past premiers, we need to adjust for changes in the game over time.

How do we adjust for changes in the game? Simple. This year, teams have averaged 89.1 points per game. Richmond's average of 91 per game is therefore 102 percent of the league average. The Tigers have conceded 74.6 points per game, which is 84 percent of the league average, bearing in mind that a lower figure is better for defensive performance. By performing this calculation for each past premier, we can figure out their attacking and defensive strength, adjusted for changes in the league.

DATA: AFLTABLES.COM

Where does that leave us? Well the Crows are clearly a strong challenger. They concede 79.1 points a game, 88 percent of the league average for this year. That's a fairly typical defensive performance for a premier; solid but not exception. It's up the other end of the ground that they really shine; their 109.8 points per game is 123 percent of the league average, an adjusted offensive performance that puts them among the strongest past premiers.

The Tigers' adjusted records are also quite respectable. A bunch of past premiers - and the 2017 Crows - have weaker defences than Richmond. The Tigers have a stronger attacking record than three past premiers, including last year's Bulldogs.

Ratings around the ground

We've looked at the two teams' Elo ratings, an overall measure of their quality, as well as their record in scoring and defending. But let's break things down a little bit more.

DATA: AFLTABLES.COM, THANKS TO HPNFOOTY.COM

How good is each team's midfield? One simple but useful measure of this is their inside 50 ratio; how many times they get the ball inside their attacking 50 for every inside 50 they concede to their opponents. On this measure, the Crows have the better record, they record 1.16 inside 50 for every inside 50 that their opponents get. That's the second-best midfield record in the league, just behind the Power. Richmond, too, is among the best in the league on this measure, recording 1.1 inside 50s for every one they give up. So the teams just about break even in the middle.

Down back, too, things are tight. Here the Tigers come out on top. On average, their opponents record just 0.42 scoring shots for every inside 50 they get against the Tigers; that's the league's stingiest defensive performance this year. But the Crows are also right up there, just a notch below Richmond.

It's up forward that the real difference between the two clubs is apparent. On average, the Crows get 0.5 scoring shots for every inside 50. That's the league's best offensive efficiency. But Richmond lags well behind, managing to record just 0.46 shots for every inside 50. That's one of the league's worst offensive efficiency ratings this year. The Tigers had a good offensive efficiency of 0.5 shots per inside 50 last week against the Giants, helped along by Daniel Rioli. Richmond's worst offensive efficiency of the season came against the Crows back in Round 6, when the Tigers managed to score just 0.28 times for every inside 50. If their preliminary final performance is any guide, they've figured out how to get better quality forward entries that are more likely to lead to shots; they'll need to be that good again up forward.

Around the contest

How good is each team around the contest? The Crows are among the best in the league at whichever measure you examine. They average 1.9 clearances more than their opponents each game - that's the 4th best in the AFL this year. They're also 4th best in net contested possessions, with the Crows scoring 5.5 more than their opponents this year. Adelaide has improved strongly in both those measures over their 2016 performance, as they have in tackles and net hit outs per game.

DATA: AFLTABLES.COM

The Tigers' record is not so great. They've been smashed in the hit outs this year, averaging a whopping 13.4 fewer hit outs than their opponents. Partly due to their weakness in the ruck, the Tigers have weak records in net clearances and net contested possessions, ranking 11th and 12th in the league in those measures. The Tigers are doing a lot of things right, but they're succeeding despite their weakness in contested ball. Still, their strengths elsewhere might be enough to make up for it, the Tigers got fewer contested possessions than the Giants last weekend, and still convincingly won the preliminary final.

The premiership quarter

The Tigers come out of the blocks strong, with a percentage of 133 in first quarter this year. They also finish strong, with 146.2 percent in final quarters. The middle part of the game tends to be the lull for the Tigers, but it's the second quarter when the Crows really get going. This year, Adelaide has averaged 171.2 percent in second quarters.

DATA: AFLTABLES.COM

On most measures, the Crows are the better team. They have a stronger offense, whether you measure it by points-per-game or efficiency at turning inside 50s into shots on goal. Their Elo rating is higher, and has been all year. Their performance around the contest is clearly better, beating the Tigers in average net contested possessions, net clearances, net hit outs and tackles per game. Despite that, the two sides just about break even when it comes to the overall midfield metric, the inside 50 ratio. The Tigers have the slightly stingier defence, one of the few areas where they are the stronger team.

But the teams are close enough to one another in quality that we can hope for a tight contest this weekend. Despite the Crows' strength, the Elo ratings system is tipping a narrow Tigers win, thanks to the benefits of playing as the de facto home team.

Matt CowgillMatt Cowgill is an economist by day and footy stats obsessive by night who thinks there's no such thing as too many graphs. He uses data analysis to tell stories for ESPN's Footy Forensics, as well as his own blog The Arc.

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