can anybody plz tel me why did this happen .....

As the copter was revolving it points towards esc failure check esc ......but not sure even bad soldaring can cause such issue or a faulty esc....i had once experienced this but was lucky that the copter was control-able in mid air

one of the very important reason would be lost contact between your tx and rx. Was this your first flight?
What about damage?

Hey,

Which radio ??
Naza v2 is a good controller... windy day.
You had gps locked ?
In the video i can see a lot of pulsing ....
You have mobile towers near by ?
Please upload the pics of the crashed quad.

i do not know what happened but you were lucky ....

it was my 11th flight ....... surprisingly there was no damage just the gimbal came out . I'm confused coz immediately after tis fall... it started flying perfectly and now i did almost 7 flights no prob but I'm just worried wat if tis happens again when its above water o sum thing .....im just trying to figer out the reason why it just suddenly fell n then working perfectly 

450 quad - multistar 2212 motors - multistar esc - 10" carbonfiber props - 5000mah 3s lipos- arris cm3000 gimbal - turngy 9xr radio , frsky tx n rx