There are good short balls and bad short balls, but sometimes their goodness or badness is an entirely post-facto construct. Take two balls Pat Cummins bowled, back-to-back, to Pathum Nissanka in Lucknow. Both were banged into roughly the same area of the pitch, and both climbed to just over shoulder height and finished outside off stump.
Nissanka pulled the first one for four, picking the length in a flash and dispatching the ball well in front of square.
The line of the second short ball may have been ever so slightly closer to Nissanka's body, cramping him ever so slightly for room, or Nissanka may have taken ever so slightly longer to get into position for the pull. In any case, he failed to get on top of the bounce, and hit the ball in the air, within range of David Warner haring to his left from deep square-leg.
Similar balls, different outcomes, and in each case there was only so much the bowler was in control of. Bowling fast is an intensely physical act, bowling fast and short even more so, and how quickly the ball reaches the batter and at what height and line are hugely dependent on the vagaries of the pitch and how the ball reacts off it.
Bowling short is, in essence, an act of faith.
The variance of outcome between those two short balls from Cummins is also typical of that length. It's a length that's likely to go for runs, but it's also likelier than most other lengths to bring wickets.
As the above table will tell you, short balls are wicket-taking balls whether you're bowling in the first powerplay or second. But it's an exceedingly risky ball to bowl in the first ten overs, where only two fielders are allowed outside the 30-yard circle - fast bowlers at this World Cup have gone at more than nine an over in this phase when they have bowled short, according to ESPNcricinfo's data. The two extra fielders allowed outside the circle in the middle overs gives fast bowlers greater leeway to bowl short. You're still likely to go for runs, but the risk-reward equation is a little more balanced.
It's why Cummins, bowling with Sri Lanka 125 for no loss, went short to Nissanka right after being pulled so dismissively. Australia needed a wicket at that stage, desperately, and Cummins was prepared to concede runs in an effort to look for one.
Speaking on the eve of his side's match against Pakistan in Bengaluru, Cummins suggested that Australia used the short ball a little more aggressively through the middle overs against Sri Lanka than they had in their previous game against South Africa. Australia conceded century opening stands in both games, but where South Africa ran away to 311, Sri Lanka collapsed to 209 all out, with Cummins providing the spark with the wickets of both openers.
Correlation does not equate to causation, of course, and the choice between bowling good lengths and keeping the runs down and going short frequently in the search for wickets is by no means straightforward.
"It's a delicate balance sometimes," Cummins said, "where you're trying to keep the run rate in check, try and go for three or four or an over, or do you try and risk it to pick up those vital wickets?
"And yeah, I think you saw a bit of a shift in this last game. You know, South Africa, we felt like we had them relatively under control, but we didn't get any wickets. Last time, last game, we were a little bit more aggressive, a few more bouncers, and yeah, fortunately got us a breakthrough, and that's kind of where you get into the game. So I think it's always that delicate balance."
Cummins isn't the first bowler you'd picture when you think of middle-overs enforcers. He has a terrific short ball in Test cricket and uses it often, but his bowling in that format - his best format - revolves around targeting the top of off stump and looking for the classic modes of dismissal - bowled, lbw, nicks to the keeper and slips. Fast bowlers can put those skills to use in ODIs when the ball is new, but Australia have Mitchell Starc and Josh Hazlewood bowling in that phase.
As first change, Cummins does a job that he isn't exactly a natural at. He isn't Lockie Ferguson, a white-ball specialist who trains year-round to bowl middle-overs lengths in white-ball cricket. But it's a role Cummins has to perform out of necessity, and a role that's vital for Australia at this World Cup, where they only have one frontline spinner with whom he can share the middle-overs wicket-taking burden.
It's also a role that's heavily dependent on what has come before. Cummins hasn't had a great World Cup, so far, in terms of the situations he's begun bowling in. There were no new-ball wickets against either South Africa or Sri Lanka, and while Australia picked up three in their opening game against India, they had only posted 199 batting first.
Pakistan and Bengaluru are likely to present Cummins with another stern middle-overs test. The Chinnaswamy Stadium is traditionally one of the fastest-scoring grounds in India, with pitches that offer true bounce and an outfield that's among the smallest in the country. The straight boundaries are particularly short, so teams often tend to try and make batters hit square.
The short ball, then, is likely to be a key component of the middle-overs battle. How Cummins uses it could significantly affect Australia's fortunes.