Colwyn police Cpl. Trevor Parham's bench trial started Thursday in Delaware County.
Parham, of Upper Darby, allegedly used a stun gun on the handcuffed teen inside a holding cell then used the acronym for "laughing out loud" in a text-message exchange with a fellow officer afterward.
The teen said he was arrested without justification but acknowledged kicking the cell and yelling before Parham used the stun gun on him.
Thomas Fitzgerald, Parham's attorney, said in his opening statement that Parham's prosecution "is politically charged and politically motivated."
Assistant District Attorney Christopher DiRosato said Parham subjected Da'Qwan Jackson to an unlawful arrest and knew it was illegal.