Rugby: visiting teams more aggressive than home teams

At least one study has shown that players on a home team will have higher levels of testosterone than players on the visiting team. Does that mean home players will be more aggressive?

Apparently it's the opposite. A study called "Game location and aggression in rugby league," by Marc V. Jones, Steven R. Bray, and Stephen Olivier, found that in British rugby, visitors committed more "aggressive behaviors" than the home side.

In order to eliminate the possibility of referee bias, the authors videotaped 21 games, and asked expert observers to look for aggression. They found 632 such acts – 306 from the home team, and 326 from the visiting team.

They broke down as follows:

137 by the home team when the home team won
119 by the visiting team when the visiting team won
140 by the home team when the home team lost
185 by the visiting team when the visiting team lost

It looks like most of the effect comes from visitors who lost. (I assume these numbers don't add to 632 because of ties.)

More interesting is the breakdown by half (again, ties excluded):

341 aggressive acts in the first half
240 aggressive acts in the second half

The authors don't do a significance test for half, but, clearly, there are more instances of aggression in the first half. I wonder if this applies to other sports. Perhaps the famed unwillingness of NHL referees to call penalties in overtime is partly due to there actually being less to call.

Broken down further:

Teams who eventually won:  165 first half,  91 second half.
Teams who eventually lost: 176 first half, 149 second half.

Almost all the difference between winning teams and losing teams comes in the second half. Perhaps in the first half, the outcome is still in doubt – it's only in the second half that the leading team realizes it's going to win, and finds it less necessary to take out their aggression.

It would have been very interesting to see whether the observers' counts of aggressive acts matched the referees' calls, but the authors don't give that information.