Identifying the DNA of a BBL Innings

Every ball counts in T20 cricket. 

It’s a statement often put forward by commentators, and, given the dynamic, fast-paced nature of the game, it's a sentiment that is difficult to argue against.

Whilst, on one hand, this may be the case, on the other, it doesn’t necessarily mean every ball in a T20 innings is created equal. The 'Power Play' and fielding restrictions that come with it are a great example of this - under the rules of the game, the baseline ‘structure’ of an innings is modified for a six over period giving the batsmen a greater opportunity to find the boundary rope.

With that in mind, we thought we’d take a look at how often each of the different ‘results’ (e.g wicket, dot ball, four, etc) have occurred at different points in the innings over the last five BBL seasons.

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This should not only help us piece together the basic ‘DNA’ of a BBL innings, but also help in evaluating player performance at different stages of a match.

Wickets

Let’s start off with one of the big ones, being a wicket. The graph below shows how often a wicket has historically occurred in each over of the BBL.

What immediately sticks out is the sharp uptick towards the end of the innings, which probably makes a lot of sense to those of you who have kept a keen eye on the BBL over the last few years. In fact, in the final over of an innings, a wicket has historically been just over 2.5 times more likely to fall than on the average ball in the BBL.


The short of all this, as a very general statement, is that we would expect bowlers being thrown the ball towards the end of an innings to pick up more wickets than their ‘middle over’ counterparts. This may, however, come at the expense of their economy rate, as we will see later on.

We can see this shining through in the BBL leading wicket-taker list, with the top four leading wickets takers in BBL history (Ben Laughlin, Sean Abbott, Kane Richardson and AJ Tye) all being noted 'death' bowlers.

Fours

Looking at how often batsmen have historically hit a four really hammers home the point we mentioned above about the 'Power Play'.

This number is at its highest during the first six overs when the fielding restrictions are in place, followed by a sharp drop as captains are allowed to place more sweepers along the boundary rope. This number then trends upwards for the remaining overs as teams accelerate towards the end of the innings.


It is important to keep this in mind when comparing economy rates of different bowlers.

If we take the hypothetical example of two identical bowlers: 'bowler A', who doesn’t come on until after the 'Power Play' is finished, and very rarely bowls in the last four overs of a game, chances are they will have a better economy rate than 'bowler B', who bowls a couple of overs at the end of the 'Power Play', then comes back on to bowl a couple more at the end of the innings.

The graph above helps to show there are more forces at play than just the ability of an individual bowler, and helps explain why bowler’s economy rates can blow out when they come back on to bowl towards the end of the innings in a T20 match.

That’s not to say 'bowler A' in the hypothetical example above isn’t, in fact, harder to score against than 'bowler B' (assuming this time they were not completely identical)  – just merely stating that context - including at what point in the innings they are bowling - is relevant to judging performance.

Dot Balls

Turning our attention to dot balls, and there is a clear downward trend in the data, with occurrences peaking in the first over of the innings before bottoming out in the 20th over. This line also helps explain why a bowler’s economy rate can blow out when they come back on for a second spell late in the innings.


The first over of the innings having the highest portion of dot balls raises an interesting strategy point that has emerged over the last few seasons. 

Some captains have been willing to give the first over of an innings to a part-timer (and in most cases, a part-time spinner).

The logic being, it is considered one of, if not the ‘easiest’ over to bowl, presumably as both batsmen at the crease may not quite have their eye in as yet, resulting in them taking a more conservative approach. This allows captains to try and rush through an over whilst conserving their premium bowling resources for later in the innings.

The graph below shows the average runs per ball scored in each over of a T20 innings. 

As we can see, that number is at its lowest and the start of an innings, before trending upwards in the later overs – suggesting captains might just be onto something here.


Like any cricket stat, it’s also important to keep the context in mind – traditionally, the first over of a match has usually been given to a team’s premier quick bowler in an attempt to take advantage of any early movement that may be available. Better bowlers traditionally bowling the first over - coupled with a swinging ball, making it harder to score - also offers a plausible explanation as to why the data is saying the first over is generally the most ‘economical’ in a T20 innings.

In reality, it’s probably a combination of these things (if not more) which lead to what the data is telling us about the first over of a match – but in any event, it’s an interesting point to keep an eye on!

Ones and Twos

Looking at the graph below relating to singles, and the first thing that jumps out is the line looks very similar to the inverse of the ‘Four’ graph from above.


With fielding restrictions in place and fewer gaps in the infield, the data is saying batsmen are hitting singles less often in the 'Power Play', before this number spikes as soon as the fielding restrictions are lifted. This makes sense as balls that may have otherwise gone for four in the 'Power Play' are now being cut-off by the newly in-place sweepers, and turned into singles or twos.

The steady decrease towards the end of the innings can also be explained in part by the ‘Two’ graph (below). 

As teams reach the end of the innings (usually with wickets in hand) they are willing to take more risks running between the wickets, putting pressure on fielders, hence shots hit towards boundary riders which may have previously been ones are getting turned into twos by the runners at the crease.

The lower occurrence of two’s in the 'Power Play' also makes sense as more shots that find the gaps and pierce the infield will reach the boundary rope, as opposed to being cut-off by sweepers.

Sixes

As you can see in the graph below, the general trend for sixes is they occur more often as the innings progresses. This is also reflected in the spike in average runs per ball scored towards the end of an innings. Again - with wickets (usually) in hand - teams seem to up their aggression and scoring intent towards the latter stages of an innings.

Another interesting point coming from the data is that batsmen (as a general statement) become more likely to hit a six the more balls they face. The latter overs of an innings provide a greater opportunity to have at least one set batsman at the crease, so that may contribute to the lines' general upward trajectory.

The low point in the first over also contributes to why it can be considered one of the ‘easiest’ to bowl in a T20 innings.

Just as suspected, the data is telling us that not every ball in a T20 is created equal. 

It will be interesting to see if these trends continue into the current season and hopefully will help us evaluate the performance of players at different stages of a match as the tournament progresses.

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Ritchie Tabor

After spending most of his life on some kind of footy field, golf course or cricket pitch, Ritchie has always had a passion for sport. A stats nerd who could recite the Australian cricket team before he could walk, Ritchie now combines that passion with looking into the numbers that make up a game.

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