A shootout in a domestic competition happens in front of a partisan crowd. At a tournament in a neutral stadium the noise is a different phenomenon, and players notice.
A neutral crowd splits rather than swells
In a home stadium the reaction to a penalty is unified: one enormous noise for a goal, silence for a miss, with no ambiguity about direction.
A split crowd produces two overlapping reactions at once, and the taker receives a signal that is loud but not clearly about him.
Several players who have taken both describe the neutral version as more disorienting, because the usual cues for reading a moment are absent.
Neutral audiences are quieter during the run-up
Partisan supporters behind a goal work actively to distract an opposing taker, and a taker's own crowd falls into a recognizable hush.
A mixed audience does neither consistently, leaving a low general murmur through the walk, the placement of the ball and the run.
That relative quiet lets the taker hear his own breathing and the referee's whistle far more clearly than he would in a league match.
Large multipurpose stadiums disperse sound
The World Cup returning to North America means shootouts in wide bowls where the seating is further from the field and the roof is open or high.
Noise escapes upward rather than reflecting back, so a very large crowd delivers less acoustic pressure to the penalty spot than a smaller compact ground would.
Players moving from tight European stadiums to these venues consistently report the atmosphere feeling different, and the geometry is the explanation.
Goalkeepers lose one of their tools
Keepers routinely use the home crowd, gesturing to raise noise before a kick and timing their movements to it.
Without a reliable crowd to conduct, the goalkeeper's pre-kick routine becomes a purely private performance aimed at the taker alone.
Some adapt by exaggerating physical gestures, which is why neutral-venue shootouts often feature more theatrical goalkeeping than league ones do.
Preparation now includes the sound environment
Teams practicing shootouts increasingly do so with recorded crowd noise, on the theory that the unfamiliar auditory setting is part of what causes failure.
Rehearsing the full sequence, including the long walk from the halfway line, addresses more of the actual task than repetition of the kick itself.
Which reframes shootout preparation as training for a specific environment rather than as practice at striking a stationary ball.