Factual error: Captain Riker and Lt. Fitzgerald are wearing their insignia, which is incorrect. Officers serving in front line units did not wear their insignia because it identified them as high priority targets for Japanese snipers.
Factual error: In his opening narration, Rod Serling says that he is quoting Shakespeare's play Richard the Third. His quotation is actually from Richard the Second, also written by William Shakespeare.
Answer: It's explained in the episode. The aliens are experimenting to see how humans react to various scenarios. This just happens to involve them using super strength.
Thanks. It's been a long time since I saw the episode so I forgot.