Strandhogg in old Norse was a Viking tactic, based on the spies followed by a flash raid, like commandos on the coast. One of its possible, but non exhaustive significance is “fight on sand or on the beach”.
It was almost exlusively a Norwegian Vikings technique of combat.
The Vikings had already developed spy networks from their many commercial counters vicus. These spies informed them of the local customs, the dates of religious feasts, helped with translation and indicated places to plunder and personalities to be removed and hold to ransom. It happened that Vikings made these raids against their own countrymen as well. Harald I, known as Harald Fairhair, prohibited strandhögg on the Norwegian territory.