American soccer requires travel that European leagues never contemplate. That schedule shifts where goals come from, and dead balls take up the slack.
Open-play attacking is the first thing fatigue removes
Creating chances from open play depends on repeated high-speed runs, quick combinations and defenders being dragged out of position by movement.
All of that costs energy that a tired team cannot spend, so attacks slow down, become more lateral and finish with hopeful deliveries.
The chances a team generates therefore fall in quality across a heavy travel stretch even when possession and territory look unchanged.
A set piece asks for one effort, not sixty
A corner requires a delivery and a jump. It does not require the sustained running that produces a chance from open play.
A tired team can execute a routine as well as a fresh one, because the physical demand is concentrated into a few seconds.
The share of a fatigued team's goals that come from dead balls therefore rises, not because they get better at them but because everything else gets worse.
Time zones affect timing more than they affect strength
Crossing multiple time zones disturbs sleep and body clock rather than muscular capacity, and the visible cost is in reaction time and coordination.
Those are exactly the qualities open-play finishing depends on: judging a bouncing ball, timing a run behind, reading a goalkeeper's position.
A rehearsed corner depends on memory and position instead, which degrade far more slowly than fine timing does.
Defending set pieces gets worse at the same time
Marking a corner requires concentration held across a long match, and lapses in tracking a runner are a documented feature of tired defending.
So the same schedule that makes a team more reliant on set pieces makes their opponents more vulnerable to them, which compounds the effect.
Matches late in a heavy travel run consequently produce more dead-ball goals at both ends than the teams' season averages would predict.
Coaches plan around this deliberately
Staff facing a difficult road stretch often front-load set-piece work in the preceding training week, knowing there will be no time to coach it on the road.
Some carry a simplified routine for tired legs, with fewer moving parts and a delivery the taker can hit without thinking.
Which turns a scheduling problem into a preparation decision, and explains why the best-organized teams lose less on the road than the travel alone would suggest.