Aggressive Opening Batmen in ODIs

After five games in the 2015 cricket World Cup, an interesting pattern is emerging: So far, the average score of the team batting first has been 323 runs (well above the historical average for ODIs), and has gone on to win the match in four of the five matches, and yet in three of the four cases where the team batting first won, it was the losing team that won the toss and sent the opposition in to bat. Captains are likely to see this pattern and adjust their strategy, but I think that would be a mistake.

One of the interesting things me to watch out for going into this World Cup was the approach taken by both the batting and bowling teams in the opening overs of the first innings.It has become conventional wisdom that in the modern game it is crucial for batsmen to be aggressive from the outset. This view is seen and heard in media commentary, and is revealed as strategy in team selections: After After playing down the order last year, Brendan McCullum has returned to the opening spot along side Martin Guptil, as New Zealand empahsise a high-risk, high-return approach to batting from the outset. Australia are opening with two high-risk, high-return batsmen, and England recently dropped their relatively conservative opening batsmen and captain, Alistair Cook and also elevated the more-aggressive Moeen Ali to the top of the order.

But is this conventional wisdom correct? Obviously, faster scoring is better for a batting team than slower, given the same likelihood of losing a wicket, and conversely less risk is better than more for a given strike rate, but what is the trade-off? Peter Miller, aka The Cricket Geek, has expressed the trade-off as follows:

In many ways, getting out for a 15-ball 30 is less of a crime than 65 off 90 deliveries. 

This captures the essential difference between test cricket (most of the time) and limited-overs cricket. In the former, time is not a constraint, so the key to a large score is to not be dismissed; 65 contributes more to your team than 30 in most circumstances. In limited overs cricket, every ball faced is a ball that is not available to your teammates. The opportunity cost of balls used up has to be weighed against the runs scored. But is Peter's summary of the trade-off correct? As it happens, there is a measure of the opportunity cost of wickets lost and balls used it up that can answer this question exactly. It is WASP. A player's contribution to his team in the first innings is the amount that WASP advances by on the balls that that batsman faces. Let's imagine that an opening batsman is the first to be dismissed having either scored 30 runs and faced 15 of the first 30 deliveries, or having scored 65 runs and faced 90 of the first 180 deliveries. Which option will have advanced WASP by the larger amount? Well that depends on whether the game is played on a high-scoring or low-scoring pitch. In 250 conditions, the more aggressive opener would have had a net contribution of just under 4 runs compared to just over 11 for the less-aggressive player. In 300 conditions, however, 30 off 15 would give a slightly negative contribution, but 65 off 90 a more-negative one. The cross-over point is when the par score is 278 (roughly).

I reckon that 280 is probably about the average par score for the pitches being played on in this world cup (the succession of first-inning scores over 300 are misleading, as in every game so far, the more-fancied team has batted first), so Peter's example is very finely calibrated but correct.

But there is a seeming inconsistency in the conventional wisdom. As the same time that the consensus is that batters need to be attacking from the outset, media commentary is emphasising the importance of early wickets. And again, this appears to be accepted in team strategies. New Zealand has expressed the intention of attacking from the outset, when bowling as well, being prepared to concede runs in the search for wickets. Australia have their bowling spearheaded by Mitchell Johnson who, it is said, may prove expensive but can also destroy a team with early wickets, and so on. That is, the conventional wisdom is both that opening batsmen have to be aggressive from the start and that it is important for bowling team to secure early wickets. But ifthe risk-return trade-off is such that the benefit of quick runs to the batting team makes it worthwhile taking the risk of early wickets, then the reverse should be true for the bowling team. In the numerical example above, while it is true that 30 off 15 is a better contribution than 65 off 90 on a 300 pitch, both contributions are negative relative to the average opening batsman performance.

Actually, the view that bowling needs to be aggressive at the outset is probably closer to the truth than the view that batting needs to be. At the start of an ODI first innings, the cost of a wicket is between 25 and 30 runs, depending on the conditions. As long as a team has wickets in hand, that cost diminishes steadily as balls are used up, and the trade-off between risk and return favours greater aggression. (Of course, balancing that is the fielding restrictions in the first 10 overs, which lowers the risk from fast scoring.)

If this combination of aggressive batting and aggressive bowling/fielding carries through, in the World Cup, I expect to see a high-variance in first-innings scores: some high scores where the aggressive strategy pays off, and some low ones where rapid wickets impose a large cost. In some cases, when a high first-innings score is achieved, the same strategy will pay off for the chasing team; when a low first-innings score is made, the chasing team should always win by being more conservative. For that reason, notwithstanding the results in the first five games, I still believe that the toss-winner should choose to bat second.* Let's see how it plays out.

* The exception to this rule is when a highly ranked team plays one who is much weaker. In this case, the crazy net-run-rate method for choosing between teams with the same number of wins and losses, implies that the better team should choose to bat first, just to make sure that they bat for the full 50 overs and have more weight on that game in the NRR calculations. But that is the subject for a later post.