A pilot observing from the ground at a non-towered airport reported observing an NMAC between a landing aircraft executing a go-around and an aircraft departing. The reporter monitoring the CTAF did not hear one of the aircraft making any position reports.

Narrative

I was not flying a plane in this incident; I just observed from the ground; all information above is my best guest as tow the specific details of the flights. I was observing Aircraft X takeoff from Runway 31 from the fence line on the southwest side of the runway. Aircraft Y was approximately midfield on their downwind leg as Aircraft X lined up for takeoff on the displaced threshold of Runway 31. Once lined up; Aircraft X waited as Aircraft Y made it through their downwind and base legs. While Aircraft Y was on final; Aircraft X began their takeoff roll. Aircraft Y added power and appeared to begin a go around as Aircraft X became airborne. Neither aircraft appeared to sidestep to either side of the runway for a considerable amount of time; and the minimum vertical separation during the incident appeared to be 100 to 200 ft. At this time I turned on the radio in my aircraft to listen to traffic in the area. Both aircraft remained in the pattern; and Aircraft X made multiple high speed low passes over the runway. During the time I had my radio on I did not hear any communication from Aircraft X; only Aircraft Y making normal traffic pattern calls.