The review system was introduced to correct obvious errors, and its largest effect has been on how spin bowling operates.
The old convention
Umpires were historically reluctant to give leg before to balls pitching outside off and turning in, or to batters well forward.
Which was a convention rather than a law, based on uncertainty about where the ball would have gone.
Ball tracking removed that uncertainty, or at least replaced it with a stated projection.
What changed
Deliveries that previously would not be given became viable wicket-taking options.
Which particularly affected the ball going straight on, and the one turning into the batter from outside off.
Bowlers who could produce those deliveries gained a mode of dismissal they effectively did not have before.
The batting response
Playing forward with the pad first became far riskier.
Which pushed batters toward playing with the bat in front of the pad and toward using the crease more.
Sweeping increased partly because it addresses the same problem differently.
Umpire's call
The provision that marginal decisions stand with the on-field call.
Which has been the most contested element, since identical tracking outputs produce different outcomes depending on the original decision.
The justification is acknowledging measurement uncertainty rather than pretending the projection is exact.
Review strategy
Limited reviews create a resource management problem.
Which means captains weigh confidence against the cost of losing a review.
Wasting reviews early leaves teams exposed to genuine errors later, and this has decided matches.
Technology limitations
Ball tracking is a prediction based on the observed trajectory before impact.
Which is more reliable the further from the stumps the impact occurs and less so for deliveries hitting the pad very close.
Published accuracy assessments exist, and the systems are calibrated rather than infallible.
Wider effects
Umpires' decision-making has itself changed, with more decisions given on the field than before.
Which is arguably the more interesting outcome — the technology altered human behaviour as much as it corrected it.
Watching a spinner bowl now, the whole set-up assumes the review system exists.
Edge detection
Audio and thermal technologies used to determine contact.
Which has its own accuracy debates, particularly where bat and pad are close together.
Different competitions use different combinations of technology, which produces inconsistent standards between series.
Cost and availability
Full technology suites are expensive and not used in all matches.
Which means decision standards vary by competition and by broadcaster investment.
This has been a source of complaint from boards with fewer resources.
Umpire performance
Published data indicates on-field decision accuracy is high and errors are concentrated in specific situations.
Which is a more flattering picture of umpiring than the review system's existence implies.
Effect on captaincy
Review decisions are made in seconds with input from the bowler and keeper.
Which is a distinct skill, and some captains are demonstrably better at it than others.
Format differences
Review allocations differ between formats, changing how aggressively they are used.
Shorter formats with fewer reviews produce more conservative usage.
Left-right combinations
Batting pairs of opposite handedness disrupt bowling lines and field settings.
Which interacts with the review system, since angles change what is possible.
Around-the-wicket angles for spinners became more common partly for this reason.
Coaching adaptation
Young spinners are now coached with the review system as a given.
Which affects stock delivery selection and how much they aim at the stumps.
The straighter ball has genuine value in a way it did not previously.
Batting technique
Getting the bat further ahead of the pad and using depth in the crease.
Which is a visible technical shift across a generation of players.
The broader effect
A technology introduced to correct errors reshaped a whole discipline of the game.
Which is the more interesting outcome and was not the stated intention.
Similar effects have followed technology introductions in other sports.
Field settings
Captains now set fields anticipating leg before appeals as a genuine mode of dismissal for spin.
Which affects where catchers are placed and how attacking a field can be.
Short leg and slip placements reflect assumptions about how batters must now play.
Format variation
The effect is largest in the long format where spinners bowl most overs.
Which is where the technical adaptation has been most visible.
Player and viewer reception
The system is broadly accepted, and the umpire's call provision remains contested.
Which produces periodic proposals to change it, none yet adopted at the time of writing.
The argument turns on whether marginal decisions should default to the on-field call or to the tracking output.
What it settled
Obvious errors that once decided matches are now corrected, which was the original purpose and has been achieved.
A final observation
The spinners who benefited most were not the biggest turners of the ball but those with the control to bowl repeatedly at the stumps and force the batter to play.