Sydney fans were seeing red, St Kilda supporters had smoke coming out of their ears and Adelaide tragics were baffled on another weekend where AFL umpiring came under the spotlight.

All teams, playing interstate against the Western Bulldogs, West Coast and Hawthorn respectively, were on the end of lopsided free kick counts - with the Swans (18-31), Saints (8-23) and Crows (11-22) all getting the raw end of the pineapple.

It left many fans, coaches and experts wondering about the effect of hometown crowds influencing umpires' decision-making, especially when a team hosts an interstate rival. Statistics do show that home teams tend to win more free kicks than visitors, but not all sides benefit equally from this skew towards the locals.

In recent years, home teams have averaged around 1.5 to 2 more free kicks than their opponents each game. Last year, the average free kick differential between home and away teams hit 2.1 - the highest figure since the early 1990s. Strikingly, in the first two rounds of the 2017 season, home teams have averaged 3.6 more free kicks than their opponents, but it's too early to conclude much from that.

Free kicks in the AFL:

Home clubs tend to win the free kick count, but not all teams fare equally well with the umpires. West Coast have done particularly well over the years, securing an average of 4.4 more free kicks than their opponents when playing at home since 2000. The Bulldogs, too, have received a sizeable leg-up - they have averaged 2.8 net free kicks in their home games this century. But at the other end of the spectrum, the Hawks at home have tended to get slightly fewer free kicks than the away team, leaving them with a negative average net free kick count; the figures for Brisbane and Melbourne are also negligible.

Average net free kicks:

Of course, we shouldn't expect free kick counts to be even in individual games. A fairly adjudicated game isn't one in which both sides walk off the ground having received the same number of frees; it's one in which the umpires paid legitimate free kicks and didn't pay any that weren't there. But it's a little surprising that some teams seem to get such an advantage when it comes to free kicks, even when we average over the 16 and a bit seasons of this century.

So why do certain teams seem to do well on free kicks? One theory is that clubs win more free kicks because they're better teams. Maybe the Bulldogs and Eagles do well out of the umpires because they play quality, clean football.