The wobble ball works because the bowler does not know what it will do either

A seam that arrives upright and stable is a bowler's decision; a seam that arrives wobbling hands the decision to the pitch.

Two balls, same bowler, same length, thirty seconds apart. The first is released with the seam locked upright and the fingers behind it, and it moves away, because that is what a stable seam angled slightly toward the slips does when it lands. The second is released with the seam rotating on an unstable axis, and it might move either way or not at all. The batter cannot pick either one. Only one of them can be picked by the bowler.

That asymmetry is the whole appeal. Conventional seam bowling requires the bowler to commit to a direction, which means a batter who has watched him for twenty minutes can commit too, playing with hands slightly ahead or bat angled a fraction, hedging in the right direction. Against a scrambled seam that hedge is unavailable, because the ball's behaviour is decided by which part of the leather happens to hit the ground.

The cost is control, and it is a genuine cost. You cannot bowl a wobble-seam ball to a plan that requires a specific outcome, so it is useless when you have a slip cordon set for the outside edge and need the ball to go there. It also does very little on a surface with no life in it, because the mechanism depends on the seam catching something when it lands. On a flat, hard, dry pitch the ball is arriving on smooth leather regardless.

What interests me is what it says about how the game has drifted. A generation of bowlers grew up being taught to present a perfect seam, and the perfect seam is now the predictable option. The skill has inverted. That happened because batters got better at reading the hand and the wrist, video is available on a tablet at the boundary edge, and any repeatable action is a solvable one.

The honest description is that a wobble ball is a bowler admitting he cannot outthink the batter and choosing to be unreadable instead. I have no problem with that. It is the same logic that makes a coin toss a fair way to settle an argument.

Bowl it on a pitch with a bit of grass and it is close to unplayable. Bowl it on concrete and you are just bowling badly with a straight face.