Ben Barba

Pressured ... teams are cautious when playing against Ben Barba. Photo: Supplied

Referees will say this is because the players from the top teams are more disciplined, while the real reason is they like to be associated with high-voltage, end-to-end, low-stoppage games.

Another verity of the modern game is that penalties often lead to tries, sometimes as high as an average of one from every three penalties. In fact, some teams depend heavily on penalties to win matches.

The Rabbitohs, who play Canberra at ANZ Stadium, Homebush, Saturday night, have scored 31 of their 114 tries from penalties.

It doesn't mean they scored on the first tackle after receiving a penalty, merely that they scored 31 times from the set of six tackles which followed a penalty.

By contrast, their opponents, the Raiders, have scored only 11 of their 117 tries from penalties.

So, if the referees don't blow penalties, South Sydney is significantly disadvantaged compared to Canberra.

There has also been a crackdown by the video referee on tries with any hint of obstruction.

The Bulldogs, who are already the most heavily penalised team in the NRL, rely on these plays for tries more than the other semi-final teams.

Even if referees are loath to blow the whistle during the next three weekends, they will continue to punish obstruction plays.

It follows that teams which don't rely on penalties and obstruction plays are well positioned to win the 2012 premiership. Usually, this means teams that take pride in their defence.

Defence at line dropouts is a good guide to a team's capacity to keep the opposition from scoring. So, too, is the number of opposition tries from penalties, because this usually means confronting repeat sets.

The Bulldogs have been forced into the most line dropouts of the semi-final teams, probably because of a preference to grubber kick against mercurial fullback Ben Barba.

The Bulldogs have returned the ball to the opposition 42 times via line kicks, yet yielded only 11 tries. And of the 158 penalties they have conceded, the opposition has scored only 18 tries.

The minor premiers, therefore, can win games on defence.

But Melbourne has the best record defending both line dropouts and penalties.

Of the 30 times they have been forced to ground the ball behind their posts, only four tries have come from the resultant set. Of the 131 penalties they have conceded, only 13 tries have resulted.

Souths have conceded only 10 tries from 37 line dropouts, on par with the Bulldogs.

They have yielded 16 tries from the 123 penalties given opposition teams, a comparatively low penalty count, suggesting referees don't like awarding extra possession to teams playing the NRL's emotional favourites.

But if referees keep their whistle in their pockets against all teams, Souths won't score tries but are also less likely to concede them.

The Raiders have yielded 13 tries from the 41 times they have been forced to return possession from line dropouts, or about one in three, compared to the Storm's one in 7.5.

Canberra has also allowed 22 tries from the 128 penalties given their opponents, the highest number of tries of the six semi-final teams.

Manly and North Queensland, who meet at Allianz Stadium tonight, are better defensively, although comparisons based on statistics taken over a season ignore the fact some teams meet only once over 26 rounds.

Furthermore, the Storm had a purple patch up to the Origin period and later lost five consecutive games, while the Raiders have had a season of two halves, suggesting recent data is the most relevant.

Both the Sea Eagles and Cowboys have been forced into 34 line dropouts but Manly has conceded just over half the number of tries — five compared to North Queensland's nine.

The Sea Eagles hold a similar advantage defending penalties. They have conceded 15 tries from the 136 penalties the opposition has been awarded, while the Cowboys have yielded 18 from only 120 penalties.

Adding up the tries conceded via line dropouts and penalties on the Storm versus Cowboys/Sea Eagles side of the draw comes to 64, compared to 90 on the Bulldogs versus Rabbitohs/Raiders side.

If referees take the traditional path of blowing the whistle less and maintaining a big 10 metres, the 2012 premier should come from the defensively tougher side of the draw.