Could be many things.
Props on wrong, motor in wrong direction, motor plugged into the wrong port, too high gains.
Also what flight control and what mode did you try to take off in. If ATTI or GPS with a lot of the FC's just whack the throttle to 51% and let it take off. A lot of times if you try and correct it on lift off you can over control it and cause a flip.
But anyways need way more info!