Part one of this two-part essay looked at how teams approached the task of balancing risk and scoring runs in the first 25 years of ODI cricket

Two thousand and five was an important year for the ICC. Its headquarters moved from London to Dubai. On the field, they issued a set of rules that would remake the limited-overs form.

Before then, ODI cricket had last changed substantially in 1992, when the ICC instituted the 15-over field restrictions. Since then, apart from the new rain-rule formula, the rules governing the game had remained the same. In this time, tactical innovations at the top of the batting order had created a middle-overs problem in the ODI game.

From 1992 to 2005 the limited-overs innings was divided into two parts. In the first 15 overs, the fielding team could position no more than two fielders outside the 30-yard circle, and of the rest, at least two needed to be in catching positions. After the 15th over, teams could place at most five fielders outside the 30-yard circle. With the field spread out after the 15th over, fielding sides were content to bowl their fourth and fifth bowlers, and batting sides were typically content to accept what was on offer.

The ICC tried to break this stalemate in two ways. First, they introduced the Supersub. Teams could replace one player in their XI during a match. The point of this rule was to allow teams to play more specialists. This rule was scrapped inside a year. It did not prove popular with the players, but perhaps it was discontinued prematurely.

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Second, elective Powerplays were introduced. The 50-over innings was divided into an initial Powerplay of ten overs, to be played under the rules for the first 15 overs under the old system. Two additional elective Powerplay blocks of five overs each were to be played between overs 11 and 50. These blocks were to be selected by the fielding captain. In each of these five-over blocks too, no more than two fielders were permitted outside the 30-yard circle, but the requirement for catching fielders was dropped. The idea was to break up the settled pattern of play in the middle overs.

Elective Powerplays were used in one form or the other until October 2012. In 2008, the batting side was given control of one of the two elective Powerplays.

In 2011 it was stipulated that the two five-over Powerplays needed to be taken between overs 16 and 40. The timing of when the Powerplays were taken became an important talking point.

The pattern of elective Powerplays suggests that on the whole, fielding teams preferred to get them out of the way as quickly as possible, while batting teams were more likely to keep them for the slog. Occasionally, batting sides took their Powerplay if they had well-set players of the right kind (capable of inventive strokeplay) in the middle, but the preferred option was to take it later in the innings. Neither side was particularly keen on breaking the middle-overs stalemate.

From 2005 to 2011, 83% of all Powerplay overs occurred between overs 11 and 20 and over 46 onwards.

After the rule change in October 2011 limited elective Powerplays to the period between the 16th and 40th overs, 89% of Powerplay overs occurred between overs 16 and 20 and 36 and 40.

Twenty-three per cent of elective Powerplays all produced at least 35 runs (seven per over); 22% produced at least two wickets. A majority (57%) produced at least one wicket.

The Powerplays may not have destabilised the stalemate, but they did shrink its remit, forcing teams to spend resources differently, at least during those selected overs. In the era of the 15-over fielding restrictions (1992-2005), 7.9 wickets fell per 300 balls. In the era of the elective Powerplay (2005-2012), this increased to 8.4 wickets per 300 balls.

The ICC also made changes to the way the ball was used during the innings. A rule mandating that the ball be changed after 34 overs was introduced in 2007. In 2011, two new balls began to be used again per innings (one from each end). The white ball would get discoloured and become hard to see later in the innings. These changes improved the game from the viewer's point of view, but it also gave the batsman a harder ball to hit, helping run-scoring.

In 2012, the ICC eliminated the elective Powerplays and instead mandated that, following the ten-over Powerplay at the start of the innings, during which only two fielders would be permitted outside the circle, no more than four fielders would be permitted outside the circle during the remaining 40 overs of the innings. This effectively turned the whole innings into a perpetual, if diluted, Powerplay.

This change in the rules meant that teams were now prepared to start with more caution than before, knowing that the boundaries would not be generously protected after the 11th over. And with two new balls in use, the ball would stay hard and white longer, and be less likely to reverse (swing).

As a result the average number of runs scored in the 30 overs (11-40) increased by 9.5 runs; for the final ten overs, the figure increased by 7.5 runs. The extra fielder in the ring increased the average runs scored after the 11th over by 17 runs. There was no accompanying rise in the loss of wickets.

The introduction of field restrictions after the 11th over in 2012 effectively dealt with the middle-overs stalemate of the pre-2005 era. The elective Powerplays had brought about a modest change in the middle-overs scoring rate. With only four fielders outside the circle, batsmen who had been content to take what was on offer from spread-out fields now had an incentive to try and score boundaries in every over.

In the pre-2005 era, the last 40 overs of the ODI innings produced, on average, 204 runs. In the era of the elective Powerplays this rose modestly to 210 runs. Between 2012 and 2015, teams scored, on average, 227 runs in this period. The combination of the extra fielder in the ring, two new balls, and bigger bats increased scoring rates spectacularly.

With only four fielders outside the ring, teams had only one fielder available to field on the boundary per quadrant (behind square and in front of square on the off and leg side respectively). As a result, teams chose to defend a particular boundary - usually either the square boundary or the straight boundary (as in the figure above). But this also meant that the length and often even the line the bowler was likely to deliver was telegraphed to the batsman, narrowing the options available to the bowler.

Under these new rules, the batsman had a strong incentive to look for a boundary every over. The age of the "agreed single" was in the past.

Ultimately this tactical problem was what prompted the ICC Cricket Committee to give the fielding side some extra cover after the 2015 World Cup in Australia, with the support of most international captains. A fifth fielder was permitted outside the circle in July 2015. The effect of this change can be seen in the reduction of the scoring rate in the final ten overs of ODI innings in the 2015-19 period compared to the 2012-15 period.

In 2015, the ICC found what appears to be a sustainable set of rules for the ODI game. Teams are built today to chase wickets and score quick runs. The restrictive, metronomically accurate medium-pacer and flattish fingerspinner have given way to the 90mph speed merchant and the wristspinner who gets the ball to dip and turn. The bouncer has returned to the limited-overs game as an attacking weapon.

It is often argued that T20 has influenced ODI cricket. So far, the 50-overs contest appears to be too long for T20 tactics alone to be sustained in it. Power-hitting depth is important, but an irreplaceable role still exists for the top-class batsman who can score steadily and survive against the attacking bowling of contemporary limited-overs bowling line-ups.

There's no real evidence to support the belief that T20 has influenced scoring rates in ODIs, apart from the fact that T20 happens to have existed during one phase of this period of increasing scoring rates.

First, ODI scoring rates increased steadily in the period between 1971 and 2007. The average runs scored per 300 balls in the 1975-79 period was 195. By 1985-89 this had increased to 222. In the 1995-99 period, it was 235. By 2005-09 it had increased to 250. In the 2015-19 period, this has increased to 271. To sustain the claim that T20 had some special role in this increase, one would have to explain why scoring rates in ODIs increased as they did before 2007.

Second, there is no significant overlap between players who excel at ODI cricket and those who do so in T20. A large percentage of the major ODI stars are not great T20 players, and vice versa. The 100-overs game demands traditional cricketing skills - the ability to construct innings and to bowl to get batsmen out - to a far greater extent than the 40-over game.

The evidence supports the view that as a contest of efficiency, the limited-overs form is, by design, structurally biased against the bowler. The longer the limited-overs game is played, the greater the probable scoring rates; or rather, the expenditure of finite resources (wickets, deliveries) will continue to become more efficient until an equilibrium is reached. This is not a natural process. It is shaped, as we have seen, by the ICC, as it updates the incentives for bowler and batsman.

In 2019 we appear to be in the middle of an era where the authorities are satisfied with the balance between bat and ball in ODIs. Currently there appear to be no areas of the 100-over contest in which teams are prepared to accept a stalemate. One consequence of this is that unless the pitch turns a game into a low-scoring one, close finishes tend to occur only in error-prone games. In most games, one of the teams has attained a dominant position by the 90th over. A close finish requires both teams to be roughly equidistant from a win in the last few overs of the game. With teams unwilling to be cautious and accept stalemates for significant portions of the innings, it has become vastly more likely that one of them will have surged ahead by the 85-90 over mark.

The next episodes in the history of ODI cricket might well involve rule changes that look to engineer closer finishes. An obvious way to achieve this would be by tweaking the rules to reduce scoring rates. One method would be to reintroduce a type of Supersub, which allows teams to play the extra bowler and use ten outfielders instead of nine. Under this rule, teams could name a specialist bowler as their 12th player. When the team bats, this player is not involved, but when they bowl, all 12 take the field. The drawback is that this will increase the advantage of strong squads (who also tend to be wealthier) over weak ones. But it may engineer closer finishes more frequently.

The current equilibrium is unlikely to be disturbed in the near future. Some team somewhere will find a new way to win, just as Bob Simpson's Australians did in the 1980s, the Sri Lankans did in the '90s, and England have done since 2015. Perhaps the 2020s will be Bangladesh's decade. Or perhaps they will be Afghanistan's.