Green’s Dictionary of Slang

1. (US Und.) a surprise, a scare, an ‘eye-opener’.

1914		Jackson & Hellyer Vocab. Criminal Sl.
1962		Ragen & Finston World’s Toughest Prison 815: riser – Anything that stirs to action.

2. (US tramp) an artificial sore.

1949

Monteleone Criminal Sl. (rev. edn).