The Pro14 (formerly Pro12) expanded to 14 teams at the start of this season and with it, introduced conferences to the league. This change also caused teams to have unbalanced schedules where a team is no longer playing every other team home and away. Most sports leagues in Europe generally run with a full round robin however american leagues tend to use some form of unbalanced schedule. In the NFL teams play 16 games for the regular season but will only play 13 of the 29 other teams. NCAA football and basketball are even worse where there are around 120 football colleges and over 300 basketball colleges that could be potential opponents. As a result determining some way of looking at relative strength is important for these leagues. I’m going to attempt to apply some of these methods to the 2017-2018 season of the Pro14 to look at the relative strengths of the teams.

The Pro14 Rules can be found on their website which outline the full conference and scheduling rules but here is a quick summary:

There are 14 teams split into two conferences of seven and will play 21 games A team will play every team in their conference home and away A team will play every team in the other conference once either home or away Teams will play two extra rival games against the teams of their nation in the opposite conference

As a result there are three main sources of imbalance between different teams schedules. The first is the difference between playing a team at home or away (or both) can make a significant difference in whether a team will win. For example the Cheetahs only lost at home twice to Glasgow and Munster but only won three away games against Zebre, Dragons and Kings. Similarly the Ospreys had the biggest difference between home and away wins, winning 7 at home but only getting 1 away win against the Dragons.

The second comes from the rivalry games. Certain nations will have weaker and stronger teams, meaning some teams will have an advantage with these enforced matches. Its easy to see that Cheetahs playing the Kings three times is much easier than Edinburgh playing Glasgow, even though both are sitting in third place of their respective conferences. The final one is pretty straight forward and just comes from the fact that there are 21 games in a season which means a team will have an extra home or away game. This could easily give a team a win and a bonus that otherwise would have been a loss. And could be the difference between table positions.

The first thing I looked at was the win percentage of each teams opponents and split by home and away. This gives a rough indicator of how difficult a given teams schedule was. It is slightly skewed that the better teams have easier schedules because they cant play themselves and vice versa but there are some interesting things of note. Benetton Treviso came in with the second most away wins with 5 (behind Edinburgh who had 6) but the above table would suggest they had a somewhat easier away schedule. Their opponents home win percentage was 62%, only behind Leinster. Ulster were the only top half team to have an opponent win percent above 50%. They had to play four of the top five teams in the combined table twice and Glasgow in one match for 9 of their 20 matches. In comparison to Cardiff, the fourth placed team in the opposite conference, who only had 7 matches against the top 5. Another important thing is how did this shape up for each conference. Below is a chart showing the averages split by conference. While it was close, Conference B had the slight edge overall and in their opponents away win percentage. However Conference A had the harder opponents away from home.



An important aspect of rugby that differs from some other sports is the inclusion of bonus points. As well as looking at straight win percentages I took a look at the average match points of a teams opponents for the 20 games. This is the points earned for a match result and not the points scored. Below you can see this plotted against the opponent win percentage for each team. Strangely Ulster had the second lowest opponents points per game (OPPG) even though they had such a high opponent win percentage. Somewhere between these two stats is a good estimation of how difficult a teams schedule was.

But how did this influence teams results. There are two stats Im going to look at for this, Ratings Percentage Index (RPI) and Simple Rating System (SRS). RPI is used in a number of American leagues to rank teams by looking at both the teams performance and their strength of schedule. Its calculated with the following formula:

RPI = (WPCT * 0.25) + (OWPCT *0.5) + (OOWPCT * 0.25)

Where WPCT is the teams win percentage, OWPCT is the win percenage of their opponents and OOWPCT is the win percentage of their opponents opponents. Its weighted to favour their opponents strength and not just to take into account a teams win percentage. In an NCAA league with over a hundred teams it can be useful to identify when a team who has a lot of wins, got them against relatively easy opponents. The separation won’t be as big for the Pro14 due to every teams playing each other at least once.

Glasgow remain top in the RPI standings but Edinburgh take a big leap into second place. They had the strongest Away RPI, partially helped by their impressive away win percentage. Leinster drop down due to playing the worst two teams in the league four times and the fact that they cant play against themselves. With the adjusted standings it would definitely look like B was the stronger conference apart from the Dragons and Kings.

Generally you could look at a teams points difference (this time in game points) to see how much better they are in a match. But once again what if they are hammering a bunch of weak teams and gaining a big point difference as a result. SRS is a way of adjusting for that by factoring in a teams schedule. The formula is:

SRS = MOV + SOS

Where MOV is average margin of victory and SOS is the strength of schedule. the SOS is calculated by the average MOV of all a teams opponents. This is an iterative process though as the SOS will adjust with each teams SRS calculation. As a result I ran this formula for each team 10000 times in order to get the results below.

Connacht came in with a -1.84 SRS but this was an improvement of 1.61 over their MOV which would suggest they had a tougher schedule reducing their point difference for the season. On the opposite end Ulster had the biggest drop from their MOV with 1.58 points. The table below illustrates the SRS and MOV scores quite well as the effects a teams schedule might have had on their performance.

I think its always important not to ignore the context of all the numbers. The Pro14 has a lot of rotation within its match day squads and events such as the Six Nations can drastically change how strong a team is on a given night. Its never going to be easy to factor those kind of things into it so we can only work with the general trends of the season. It will be interesting to see if the extra home/away game has any effect after this weekends games and to see if it could have changes. So while I cant make any conclusive statements on which conference is stronger or which team had the hardest schedule I’m hoping that some of this can help you in making that decision for yourself. Or at least allow you to show some evidence when you are in a heated discussion in a pub.