The last time I stretched my arms first and my legs second, I won my race. So that stretching sequence must have increased my speed. Which informal fallacy is committed in the above statement?

Crediting the win to the stretching sequence commits the post hoc fallacy.

Post hoc ergo propter hoc infers cause merely from one thing preceding another.

The stretching happened before the win, but sequence is not causation.

A single prior event gives no evidence that it produced the result.

Mistaking temporal order for a causal link is the post hoc fallacy.