Can they frisk me for no reason?

No. A frisk requires a lawful detention, and then something more — specific, articulable reasons to believe the person is armed and dangerous.

Mere nervousness, or presence in a high crime area, standing alone, is generally not enough. Those facts appear in report after report precisely because they're easy to write, and courts have repeatedly found them insufficient by themselves.

What can support a frisk: a visible bulge consistent with a weapon, a reported weapon, furtive movements toward a waistband or under a seat, or the nature of the suspected offense itself.

The two-part structure is what makes these challengeable. An officer may have had a perfectly good reason to stop someone and no articulable reason to pat them down. Those get run together in testimony, and separating them is often where the motion is.

If a frisk turned up evidence, the question is what specific facts the officer can point to for the frisk itself.