1. In a way that was not expected
   - out of the blue 
2. Without advance planning
   - by chance, accidentally, circumstantially

See also: unexpected

• punch pliers
• punch press
• punch-drunk
• punch-up
• punchayet
• punchball
• punchboard
• punched card
• punched tape
• puncheon
• puncher
• Punchinello
• punching bag
• punching ball
• punchy
• punctate
• punctilio
• punctilious
• punctiliously
• punctiliousness
• punctual
• punctuality
• punctually
• punctuate
• punctuated equilibrium