The sudden downpour of rain that hit the race on the 30th lap at the Brooklyn Street Circuit precipitated leader Nick Cassidy aquaplaning into the wall at Turn 6, into which di Grassi followed him.
Stoffel Vandoorne then also crashed into the stricken pair of cars, which ultimately caused the red flag that put the race on ice - before the decision was made not to restart.
Di Grassi said that prior to the incident, he had been on the radio complaining that conditions were "undriveable" before the crash unfolded between the trio.
He reckoned that he'd collided into Cassidy's car at around 100kph, and praised the safety structures onboard the Gen2 Formula E cars that meant all three drivers walked away unharmed despite significant damage. "The cars were aquaplaning too much, even on the straights we had aquaplaning.