step on

To adulterate (a drug) for the purpose of increasing its bulk, and therefore the profit when sold; to dilute, cut.

To oppress or mistreat (a person).

To interrupt, overpower, or override (another transmission on the same frequency) with one's own transmission.

To approach as to confront or fight.

To intrude on someone else's turf or portfolio.

Used other than figuratively or idiomatically: see step, on.