What is the impact of the Impact Sub?

Strike rates are rising - but is it only due to impact subs?

Yesterday, Sunrisers Hyderabad hit the highest ever IPL total against Royal Challengers Bengaluru. Their score of 287-3 batting first beat the next highest IPL score by 10 (also set by them this season).

The days of T20 teams rarely getting past 200 and it basically being virtually always defendable feels a long time ago, but it really wasn’t. The last two years in the IPL have shown dramatic increases in boundary percentages, and therefore strike rate, because the two metrics are extremely closely correlated.

This is clearly shown by the chart below, which shows continual growth year on year across the last four years of the IPL for these two batting metrics (2024 data includes all matches prior to SRH vs RCB yesterday).

The impact sub will have had some effect on these figures.

One considerable benefit of an impact sub for batting teams is clear - the extra batter who can play has brought has created a safety net for teams knowing they have additional depth.

Another is the greater facilitation of players to play in roles which suit their super strengths - as an example, it’s now easier to hide pace hitters who are weak against spin from opposition spinners because the impact sub allows them to have a later entry point in their teams innings.

On a side note, being able to do this can skew a player’s numbers which may not be able to be replicated in a different role at a different team, and teams would be well served to consider this when recruiting players.

These factors have contributed to considerable intent increases in all phases overall. Boundary percentages in the Powerplay have risen around 4% compared to 2022 (the last season before impact subs), which works out to around 1.5 additional boundaries in the phase.

In the middle overs (overs 7-15), boundary percentages have risen around 1% compared to 2022, equating to roughly 0.5 additional boundaries in that phase. Across the last five overs, there are 2% greater boundaries being hit this year compared to 2022, which works out to 0.6 extra death over boundaries in an innings.

Add those together and each team is, on average, hitting close to three boundaries extra per match (for example, 2 x 4 and 1 x 6 would equate to 14 additional runs) compared to in 2022, which is a critical season to compare with because it was the first year with the expansion to 10 teams but without the impact sub rule.

It’s also worth noting that there has been evidence of increased aerial intent, which is probably partly due to the impact sub (as well as other factors such as an increased level of intent overall in the domestic player pool, plus the expansion to 10 teams which I’ll discuss shortly).

This has been shown when looking at the 4:6 ratio in each year so far, illustrated here.

So, this season so far, a six is scored for every 1.7 fours, while in 2021 a six was scored for every 2.25 fours. So sixes are being hit more frequently in relation to fours.

Interestingly, there was a marked difference between 2021 and 2022 which leads me on neatly to bringing up a key point in terms of understanding reasons for why there has been such a dramatic increase in batting intent in the IPL in recent seasons.

2022 was the first year with 10 teams following the addition of Gujarat Titans and Lucknow Super Giants, and showed marked change in the 4:6 ratio. My perception is that the expansion to 10 teams has diluted the quality of bowlers available to teams, and they’re now being hit for more frequent boundaries.

Let’s have a look at how the necessity to play domestic players has changed in the IPL in recent years.

In 2021 (8 teams) with a 7 domestic and 4 overseas split, 56 domestic players used in each round of matches.

In 2022 (10 teams) with a 7 domestic and 4 overseas split, 70 domestic players were used in each round of matches.

In 2023 and 2024 (10 teams) with a 7 domestic and 4 overseas split plus an additional impact sub who cannot increase the overseas quota, 80 domestic players were used in each round of matches.

So, currently 24 more domestic players are being used in each round of matches compared to in 2021. Put bluntly, that’s the ‘next best’ 24 domestic players now playing regularly in the IPL. It’s very difficult, if not impossible, to sustain the quality of the player pool with such dilution of talent.

Essentially, these numbers show that the best batters are now fortunate enough to face worse bowlers more regularly. They are able to hit more boundaries because the balls that they are facing aren’t as good as they were before.

This assertion is backed up by the fact that balls per dismissal each season has stayed broadly the same, fluctuating between high 18s and high 19s each year across these last four seasons. So, bowlers are taking wickets at a similar strike rate, but getting hit for more boundaries.

Moving forward when assessing bowlers, we may have to start looking at reframing expectations of what is a good level of performance. We might have to make peace with the fact that pace bowlers who have a season economy of nine runs per over conceded might be perceived to be ok.

Comparing players to benchmarks is always a valuable piece of analysis, but it’s not necessarily something which many commentators, and indeed, teams, might not do much work towards. So there could be plenty of mistakes made given the need to reframe those expectations.

A lot of people have asked me whether the IPL should allow teams to play five overseas players, and I do think that it should. This would then bring down the domestic players per round to 70 (7 domestic, 5 overseas) which gets us back to the 2022 figure before the impact sub rule was implemented.

Also, I’d like to see a change to the rule which currently allows teams being able to name their starting XI after the toss. This has led to teams making quite formulaic impact sub decisions such as teams batting first picking an extra batter to start with and then subbing them off at half time for an impact sub bowler.

I’m always in favour of teams having scope to increase their tactical advantage over their opposition, and a requirement for IPL teams to name their team before toss would reduce the current formulaic nature of the impact sub.

It would allow teams to have more ability to out-think their opposition, and create more talking points as well, which can only be a good thing.