A prang is a crash.
Prang = crash
I pranged it = I crashed it
After pranging it = After crashing it
It's the sort of word that you will hear 'stiff upper lip' RAF pilots using in 1940s war movies. Other archaic terms that we use are:
I had a bit of an off - I fell off
I bailed out - I jumped off
I binned it - I crashed it
it let go - I crashed it but I'm blaming the bike for losing traction

GC