Volleyball Basics - Rotations, Side Out Percentage

In my opinion, one of the most useful volleyball stats for coaches is side out percentage (SO%). SO% is simple. It is points scored on serve receive divided by total attempts. It is a simple stat to record. One coach or player simply records a 1 for point on serve receive and a 0 for a point lost on serve receive. After the match the total number of 1's and 0's is recorded, the 1's are divided by the total of both numbers. That's the SO%. The same can easily be done for the opponent to get your team's scoring percentage, or their SO%.

In the recent NCAA women's tournament championship match, the AVCA twitter feed featured some stats from the match collected by Data Volley. One that immediately stood out to me was this one:

Nebraska side out at 66% Texas at 59%

— AVCA (@AVCAVolleyball) December 20, 2015

Something I heard many years ago about SO% is that two teams with the same SO%, let's say 50%, played each other 30 times, each team would usually end up with 15 wins. If one team improves to 51% and holds the other team to 49% and they play 30 times, the team with the 51% improves to 20 wins. That's a big change in the outcome of a season from a small change in team performance. I have run computer simulations of these scenarios and the win numbers are supported by the simulation data. The simulation numbers were a little off, but they're close enough. Side out percentage is a simple to measure stat that gives actual meaningful information.

A simple way to get even more information is to record SO% by rotation. There are six rotations and each one will have its own SO%. This information will give coaches a quick idea of where the team does well and where it struggles. Two simple ways this information can help in coaching is to give information about where the team can improve and to help decide about which rotation is the best one to start each set.

One way to use SO% to improve is to play games with the team in a rotation where they struggle and try to score some goal number of points out of ten tries. If your team has a 60% overall SO%, your team might have a goal of 6 points out of 10 attempts for those problem rotations.

Side out percentage should be taken into consideration when deciding on which rotation to start sets. The majority of teams I have coached against have started in rotation 1 with the setter as the first server. If that rotation or one soon after has a bad SO% it could cost the team over the season. Running computer simulations of matches starting at different rotations using real by rotation SO%, my teams could realistically win another match or two by starting in the right rotation. Matches rarely have teams play each rotation an equal number of times. Starting with your best rotations make it more likely to give those better rotations more opportunities. It isn't a huge difference, but over many matches it can add up. Against an opponent that is otherwise very close to your team this could make the difference. Another consideration is that any time your SO% is above 50%, it is more advantageous to start matches in serve receive than with the serve. Possibly the only place I would still want to serve first is if my best server is also at the beginning of our best serve receive rotations.

Side out percentage is one of the easiest stats to collect, even with pen and paper, and it is very useful for coaches. I recommend using it to make coaching decisions for practice design and competition choices. Small improvements in side out percentage can make a huge difference in your season wins and losses. Making the right decisions as far as something as simple as which rotation you start each set could mean another win or two.



Volleyball Basics are intended to present some of the fundamental volleyball knowledge that everyone serious about the sport should know.