Winning and Score Prediction - The working of WASP in cricket
For years while watching limited overs cricket, we have seen projected scores at different intervals being displayed on our television screens. But in the New Zealand vs India match today, we saw something different in the form of WASP (Winning and Score Prediction). Here, we have a look to differentiate between the two and explain what WASP brings to the table.
Projected scores are completely based on runs scored and looking at different totals at the end of an innings, using various run rates. For example, if a team’s score is 200 at the end of 40 overs. There could be four variations of projected scores:
- Current run-rate: 250
- 6 per over: 260
- 8 per over: 280
- 10 per over: 300
Such projections do not bring in the quality of the bowling team, it doesn’t bring in the equation of wickets left and many other parameters into the picture. The only thing it is concerned with is the run rate at which the batting team is going at. In addition, projected scores are displayed only in the first innings of a limited over match.
WASP, on the other hand, differs and gives us a predicted score in the first innings and the probability of a team winning the match in the second essay. It doesn’t just take the match situation into the equation but also factors like the team’s past record are very important parameters in its calculation.
For example, take a India vs Kenya game where India need 100 to win in 10 overs with 5 wickets in hand. In a normal match situation between two closely-matched teams, the bowling team will be favourites there but with India being a much superior team, WASP would give India a higher probability for victory.
Also, this system takes the pitch and conditions into consideration. Hence, if India need to 100 to win from 10 overs in the sub-continent – the WASP percentage would be much higher than when India find themselves in a similar situation in a country like South Africa, where the Men in Blue have a poor record against the Proteas in limited overs cricket.
New Zealand’s premier cricket broadcasting channel Sky Sport have been using WASP for over a year now.
This is how Dr Seamus Hogan - one of the creators of WASP - described the system:
Let V(b,w) be the expected additional runs for the rest of the innings whenb (legitimate) balls have been bowled and w wickets have been lost, and let r(b,w) and p(b,w) be, respectively, the estimated expected runs and the probability of a wicket on the next ball in that situation. We can then write
V(b,w) =r(b,w) +p(b,w) V(b+1,w+1) +(1-p(b,w)))V(b+1,w)Since V(b*,w)=0
where b* equals the maximum number of legitimate deliveries allowed in the innings (300 in a 50 over game), we can solve the model backwards. This means that the estimates for V(b,w) in rare situations depends only slightly on the estimated runs and probability of a wicket on that ball, and mostly on the values of V(b+1,w) and V(b+1,w+1), which will be mostly determined by thick data points. The second innings model is a bit more complicated, but uses essentially the same logic.