Sucker punches can seem like the fight starter, and are often the fight ender.
I put together this video of 12 sucker hits made on my Sim Days so that people could look at the body language and pre fight posturing of the attackers (7 by DART Instructor Chris Nicholls, 3 by senior DART students, 1 by a Ju Jitsu Instrucor and 1 by a guest Karate instructor) and the physical and verbal telegraphs they were about to attack. On the flip side of the coin, and perhaps more importantly, the mistakes in positioning, body language, fence and lack of preempt that opened up the victims.
I'm actually featured getting sucker punched here, starting from a disadvantaged position to replicate a mistake I'd made earlier in order to practice an escape. :)