This is an exciting phrase which can be roughly translated as ‘turning the tables with a single successful move/shot/blow.
一(ichi) = It expresses ‘one’ or ‘single’
発(hatsu) = It has a lot of definitions but in this context, it means ‘shots’ or ‘blows’ (punches)
Therefore…
一発= Single shot/blow
逆(gyaku) = It literally means ‘reverse’.
転(ten) = This character has a lot of meanings too. However, in this case, it implies ‘turn around’ or ‘revolve’.
So…
逆転 = come back from behind and win
Finally
一発逆転 = Coming back from behind and winning with one shot/blow. This phrase expresses dramatic turn of events or turning the tables with a single successful move/shot/blow.
If you are interested in these Kanji, you may simply copy them from this website and use them as you please. Make them yours!