Shorting Substitute Goalkeepers

SportStack has been operational for a little over two weeks, and we’re loving the interactions on social media! AlphaStack has been up and running for ten days or so, and we’ve been really pleased with the interactions we have had!

Everyone is working out their strategies, and one that has been discussed on Twitter already looks at shorting/selling the substitute goalkeeper. The basic strategy is to sell the substitute keeper once the teams have been named, and make a profit as he is likely to stay on the bench, eg selling Claudio Bravo for 3p just before kick-off, and keeping all that money. The risk, of course, is that he gets subbed on and you get hit with a big loss.

In true AlphaStack style, we’ve done some research and analysis on this strategy and have some thoughts to share (scroll to the bottom for a quick list of pros and cons).

First things first – can the strategy actually make any money? We have looked at data from the last four seasons, and believe that, yes, the strategy can be profitable! Since the beginning of the 2015/16 season, there have been 1,679 matches played, and only 28 substitute goalkeeper appearances – this gives a long-term average GK sub rate of 1.7%, meaning the win rate is 98.3%. It is interesting to note that so far this season we have already seen more GK sub appearances than in each of the last two seasons! While this might look off-putting, statistically it is highly unlikely to carry on, as there is no obvious reason for there being more injuries/red cards for goalkeepers this year (even if we would all like to blame VAR).

Using a probability of winning of 98.3%, we can calculate some expected values for the strategy, shown below. The left-hand column is the price you sell the sub GK at pre-game, and the top row show the price you have to cash out at if the GK is subbed on. The heatmap shows the profit you could expect to make from 100 trades at these prices, assuming the 98.3% win rate calculated above.

As we can see, even allowing for selling GK shares at 1p and having to buy back at 45p if it all goes wrong, the strategy can be profitable. It is important to note, though, that this works because of the law of large numbers – you will sustain the odd large loss, but in theory the gains from selling sub GKs in other matches should cover it.

So, the strategy makes money, if implemented well. This is a win, right?

Technically, yes. Statistically, yes. Financially, maybe not.

The issues of opportunity cost and account liquidity are significant.

Opportunity cost is the question of, by doing one thing, what else are you missing out on? If you commit money to shorting substitute goalkeepers, what other trades will pass you by? When you consider that selling a sub GK at 5p (which is pretty high from what we’ve seen), you need 95p in your account to fund the trade, as that is your exposure. To take the strategy on in any volume then, you need a lot of money in your account for only a small percentage gain, and this money cannot be put to use on other trades until the game is complete.

If you are betting passively, ie you’re not interested in trading in-play, this is less of an issue; but if you do want to trade in play, do you really want to tie up £95 for the sake of making £5 at full-time?

This is also based on the assumption that there’s liquidity in the market for substitute keepers, recently we’ve not been seeing too much in the way of open ‘sell’ orders available for keepers! This does not mean that in the future, there won’t be the liquidity. Remember, the platform is growing day by day.

AlphaStack thoughts

So it’s a valid strategy – it makes money, and that’s what were all here for. But for it to make money, you’ll have to stomach some big losses, and have faith in the historical data – we understand the opening part of this season would’ve been a difficult period running the strategy!

In reality though, there are perhaps better ways to make money at present. By committing a lot of capital to shorting sub goalkeepers, traders will be missing out on more lucrative opportunities. Don’t discard this one completely, as platform growth could make it more viable in the future, but for now selling sub GKs probably isn’t worth it.

Pros

  • Profitable when implemented regularly
  • Can be used passively (although if it goes wrong, you’ll want to try and trade out ASAP)

Cons

  • Not for the faint-hearted, as large losses are hard to take
  • Liquidity not available at present
  • Requires a lot of money to implement, and so opportunity cost should be considered

#SportStack #Football #Goalkeepers

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