STATS: Assessing goalkeepers in the PSL this season

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The 2019/20 PSL’s race for the Golden Glove (most clean sheets by a goalkeeper in a season) is just as tight as the race for the Golden Boot (most goals scored by a player).

Goaltenders, goalies, netminders, shot-stoppers – these are different terms used to describe a football team’s “last line of defence”: the goalkeeper.

The traditional method for assessing the performance of goalkeepers is usually clean sheets, while more advanced metrics like saves and save percentage are now also increasingly used. Locally, clean sheets remain the most accessible and common statistic to use.

SuperSport United skipper Ronwen Williams won the Golden Glove award last season, after keeping 12 clean sheets throughout the campaign. The newly announced Supersport captain is currently the leading candidate for the same award this season.

He has already kept 11 clean sheets, and has six games still to play. One advantage Williams has over his rivals is that he certainly gets more “opportunities” than them.

100% – Since the start of last season, Williams has played every minute of every league match played by SuperSport (54 matches) – the only player to do so for their club.

Clean sheet count

Altogether, 37 keepers have been used by clubs this season, with SuperSport the only club that have used just one. The majority of clubs have used two keepers, and Bidvest Wits, Kaizer Chiefs, Highlands Park, Golden Arrows, Bloemfontein Celtic and AmaZulu have used three. Whereas outfield players are interchangeable (usually within the parameters of defence, midfield and attack), the goalkeeper position is a specialist position, where only a goalkeeper can replace another. Chances for reserve goalies are rare, so rotation can be done to give other players a chance. More often, it is done because of injury to the Number 1.

At the top of the clean sheet charts with Williams are Maritzburg’s Richard Ofori (10 clean sheets with 6 games to play) and Chiefs’ Daniel Akpeyi (9 clean sheets with 8 games to play). Should they feature in the remaining games, the Golden Save race may also go down to the wire.

Clean sheet percentage

As noted, not every keeper gets the same amount of time to prove themselves. Calculating the percentage of clean sheets relative to matches played may give us another insight into goalkeeper performance. It is still within the clean sheets realm, but can give an alternative perspective.

For example, Itumeleng Khune (Chiefs) and Bongani Mpandle (Maritzburhg) only featured twice this season and never conceded a goal. This means they had a 100% “clean sheet rate”. Where do they rank, then? Because they appeared in a small number of games, this stat may be misleading. To smooth things out, we’ve calculated this clean sheet rate only for players that have featured in 500 minutes or more.

Again, Williams, Ofori and Akpeyi are up there in the rankings, but Chippa’s Veli Mothwa (57%) and Wits’ Ricardo Goss also feature in the Top 5, even higher than the three aforementioned Golden Glove contenders.

Goals conceded

A third way to assess goalkeeper performance is by focusing strictly on the number of goals conceded (which itself is a variation of clean sheets). Williams has actually conceded 21 league goals this season. On the one hand, this is the 5th highest of all keepers, and not a good reflection on the keeper & his defence.

Yet, because Williams has played in every game this season, he can also be said to have had more “opportunities” to concede. In this case, minutes per goal conceded could tell a more accurate story. This focuses, not just on goals conceded, but also takes into consideration that some keepers play more than others.

A higher minutes per goal conceded rate means a keeper conceded goals less often than his peers, and is another indicator of how well he is performing. Sfiso Mlungwana tops the charts here, conceding a goal every 158 minutes on average. Goss, Dennis Onyango & Brandon Petersen also rank highly.

A lower minutes per goals conceded rate indicates that a keeper concedes very often. For example, George Chigova at Polokwane City and Jonas Mendes conceded a goal every 61 minutes (which equates to roughly 1,5 goals a game).

Analysing goalkeepers using stats must take into consideration more than just clean sheets.

All in all, it is important to note that a team’s whole defence is responsible for keeping a clean sheet and also for conceding a goal. The goalkeeper, although he is the last line of defence, is still part of the collective. Clean sheets are an important performance analysis tool, but using any statistics devoid of context (like singling out keepers on clean sheets) doesn’t really tell the whole story. Our future analysis will go deeper into saves, save percentages and more.

RELATED STORY: Ronwen Williams: turning tragedy into success

By Opta Jabu

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