What Makes Slower Balls Effective?

A rudimentary exploration of some slower ball trends.

The slower ball is one of the prominent variations in the arsenal of a T20 bowler, but this changeup delivery gets a fair share of criticism - its overuse is bemoaned by keen observers of the shortest format, where high pace is emerging as the newest trend in fast bowling. Why do fast bowlers continue bowling them then? In a format tilting more towards hitting every single day, any sort of deception is useful to the bowler. This is even more starkly important in the game of pace-hitting: the timescales are so short that even a slight deviation can get you a mishit.

A slower ball basically is an attempt to bowl at a lower pace given the same arm action. It is well-known that batters pick cues from a bowler’s action before and after delivery to set themselves up. Therefore, maintaining the same arm speed becomes paramount in deceiving the batter. The action cues signal to the batter that a fast ball is coming, but the resulting delivery is slower. This is accomplished by somehow altering the contact of the ball with the bowling hand. In some way, the bowler breaks the transfer of energy from their arm to the ball - either cut the ball, or hold it with the knuckles, or hold it in the webbing. The slightly slower pace will ideally surprise the batter - who is too late to adjust their bat speed, and will mistime the ball.

This beautiful and skillful variation employs not only change in speed, but also dip and cut off the pitch to fox the batter. An illustration of this symphony lies in studying Harshal Patel and why he’s been so effective. This thread illustrates how all these work in symphony to induce a mishit.

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Egged on by an exploration of Harshal’s deliveries, and a conversation on Twitter where the ever so insightful Dweplea pointed out that Bumrah’s great record against lefties at the death is probably down to his brilliant off-cutter, I decided to check out a few basic elements of slower balls at the death. In the following analysis, I have taken recorded slower balls from pacers in the death overs (17-20) in all of the IPL, where I define slower ball as having a speed less than 125 km/h. I’ve chosen the over slot so that we can look at run and wicket rates without having to control for innings phase.

Good Areas Are Important

To begin, where are slower balls bowled. In the following graphic, all batters are treated as RHB, and the boxes show the percentage of slower balls bowled at that line and length. The most popular line is between the 4th and 5th stumps, and the most popular lengths are between 6-8 metres from the stumps. There is also that extremely wide and slightly short region where 5.2% of slower balls are bowled, presumably to keep the ball away from the batter’s hitting arc. In makes sense that the most frequent lines are wide - away from the bat swing, and the frequent lengths are between good and full, attempting to draw out the big shot in the slot in hopes of a mishit.

Now let’s look at where slower balls are most effective compared to fast balls, both in terms of run concession and wicket taking ability. The graph below shows the difference in RPO between slow and fast balls, grouped by line and length. A negative value means slower balls are better. The data shows that the ideal slower ball is wide in the 4-6 m zone, which makes it the toughest for the batter to hit. This makes sense: the farther away the hitting point is from the batter, the more the chances of a mishit if they have to adjust their bat speed. The 4-6 m length ensures that batter is drawn onto the front foot and is loaded up for a big swing, making changes difficult.

Also, going short and wide is generally a very bad idea. The batter has time to sight the ball and adjust, and the ball often sits up for them to free their arms.

If you’re going for the slow yorker, aim for the stumps or go really wide.

What about wicket taking? The plot below shows the difference between the wicket rates (wickets / 100 balls) on slow and fast balls. A positive value means slower balls are better. Surprisingly, almost all zones show an advantage for slower balls. Here too, we see that zoning in on that 4-6 m length is the most beneficial. Since the slower ball aims to get mishits, it’s paramount to entice the batter into hitting the ball hard. That is what that 4-6 m length does. Slower balls are good, but you need to be skillful enough to put them in the right areas while also doing whatever jiggery-pokery you’re doing with your hands/fingers to release the ball.

Loss of Pace

Of course, the change in expected speed is not the only challenging aspect of facing a slower ball. Often, you might know a slower one is coming, but the fact that bowlers usually impart some spin on their slower deliveries makes them lose pace off the surface. And this is the hardest thing about hitting a slower ball well. As a batter, you calibrate your hitting based on the pace of the pitch. A slower ball slowing down massively upon pitching messes with those calculations that your brain has already done. This makes your bat speed too fast for some balls, making you mishit. This is why pitches with inconsistent pace, like the Chennai surface, are so tough to bat on.

A slower ball loses more pace off the pitch on two accounts. It has less pace to begin with, which means it stays in contact with the ground a little longer, letting friction impede it for a little longer. It also has revolutions on it like a spinner’s ball, increasing friction and the loss of energy off the pitch. The graph below shows a probability distribution of the loss in speed after pitching for slow and fast balls.

All deliveries lose speed on bouncing, but slower balls lose noticeably more. This slight discrepancy makes them tough to smash out of the park. How can this loss in speed be employed well by an aspiring slow-ball exponent? The answer lies in the fundamentals: bowling the right length. As I said before, inducing a big shot is important to the process of deception on slower balls. The graph below shows that the average (runs/outs) decreases drastically as the ball loses more speed off the pitch for balls pitching in the 4-8 m length zone. The data shows that the loss of pace is indeed an important factor in slower ball success.

On the other hand, if you bowl short, you’ll get punished harder the more the pace lost by the ball. This is because the ball sits up, giving the batter time and space to hit it.

Lateral Deviation

Because bowlers usually implement slower balls by some sort of spin-like hand action, either off-cutting or leg-cutting the ball, these deliveries also turn off the pitch. The plot below shows the distribution of deviation (turn) from the pitch in degrees for fast and slow balls. It shows how slower balls have more extreme deviations. It also shows that more slower balls are bowled leaving the batter, which should be the ideal strategy.

What effect does deviation have? The next plots show the variation of RPO and wicket rate with the deviation off the pitch. A negative value of deviation means the ball leaves the batter. In terms of run scoring, extreme deviation both inward and out lead to curtailment, as is expected. But for wicket-taking, the outgoing delivery is most effective, as it leads to higher chances of mishits as batters hit “against the turn”.

Dip

Finally, because there are forward revolutions on most slower balls, these balls also have dip. Dip is the effect that pulls the ball downward in addition to gravity. It results from the motion of the rotating ball in the air.

The cricketing effect of dip is to make the ball land slightly earlier than it would had there been only gravity.

In the illustration below, this ball from Ashwin to Roston Chase has a dip of 0.5 m/s^2, pulling it downward with an extra force. This makes the ball land earlier and shorter: by 1.1 metres. This deception of length is instrumental in making the batter mishit the ball, like we saw in the Harshal example above, because it changes the distance between pitching and bat contact, making the ball deviate more between the two points.

Anyway, so how much do slower balls dip? Below is shown a distribution of the vertical acceleration of balls, with gravity subtracted out. This enables us to more clearly see the presence of dip (and its alter-ego lift).

Most fast balls from pacers get lift, because pacers backspin fast balls. The orange curve shows this: most fast balls have a positive value of vertical acceleration, which means they are being pushed slightly upward in the air, in addition to being pulled down by gravity. On the other hand, slower balls (blue curve) have dip (negative acceleration) on almost 40% of deliveries.

Can the benefits of this dip be seen in the data? Yes! As the figures below show, the higher the dip (more negative the acceleration), the lower the RPO, and the higher the wicket rate.

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So there we have it. A slower ball is not just about the change in pace, but a concert of various factors that flummox the batter and wrong-foot them in terms of timing and contact. The first key to good slower balls is the right areas, which draws the batter out to hit a high-energy, high-risk stroke, increasing chances of a mistiming if the bowler does execute the other aspects well. These other aspects are break off the surface, dip in the air, and a good loss of pace.

In all of the IPL, I counted bowlers who have bowled 60 or more slower balls at the death on record. Here are their RPO and wicket rates:

And here is their deviation off the pitch and their speed loss (more negative = better).