Gainer Flash
Performing tricker: bam.defocus
The Gainer Flash is a backflip of one leg that is swung into. You don't need to know how to do a backflip first, as you can slowly progress into this trick, going from vertical to horizontal and then finally to performing it fully inverted.
The easiest way to progress into this is to think about it as an Aerial that is swung into.
You can also learn the 'cheat gainer' first, which is a Gainer Flash that is kicked over the side, basically a Swing Butterfly Kick.
The term 'gainer': In Freerunning and many other sports, the term 'gainer' is used to describe a backflip that is traveling forwards. A backflip that is 'gaining' distance. In tricking however it is used to describe any kind of backflip off one foot. This leads to a lot of confusion between trickers and other athletes - for instance when Vellu landed Trickings first Double Gainer and many didn't want to acknowledge it as a real gainer.
The J-Step
The J-Step is the most common setup for this trick. It provides a block for vertical momentum and a swing for flipping momentum. Step out with your swinging leg and then step forward with your jumping leg, with your toes pointing to the side. Kick the swinging leg up to the opposite shoulder while you simultaneously swing your arms parallel to your leg.
01 Tsunami
The first progression is the tsunami kick - once again. This does not look like a gainer in any way, but it is actually very useful to learning it.
02 Tsunami no Kick
Now do the same but do not kick out. So it's just a stepover with a hop.
03 Swing into it
Now instead of stepping over, you swing over with a straight leg. Swing your arms in motion with your leg. Almost looks like a gainer?
04 Butterfly Kick
The butterfly kick is needed for the next progression. It's quite easy and leads to a lot.
05 Swing into it
This next step is also called 'Slant Gainer' or also 'Cheat Gainer'. It looks hard but if you look closely, it's just a Butterfly Kick that is swung into. So basically do step 03 but think 'butterfly kick' after you swing over.
06 Aerial
You see where this is going to. So the inverted version of the butterfly kick is an aerial. The B-Kick is to an Aerial what a Slant Gainer is to a Gainer Flash. If you want to know how to turn your B-Kick into an Aerial click HERE.
07 Swing into it
The next Step is the actual Gainer Flash. As you see now it's actually an Aerial that is being swung into. So it does not have to flip backwards completely. You kick over diagonally over your opposite shoulder and perform an Aerial. Try to spot the ground as early as possible after you leave the ground.
08 Look backwards
The last step already counts as a Gainer Flash but of course you can also flip backwards all the way. The only thing you need to change from the last progression is to throw your head backwards right after you leave the ground. The rest is the same.
Tips
Swing your arms in motion with your leg. It will give you a lot more power.
Drill the "swing butterfly kick" a lot and invert more and more as you practice.
This is a great trick to get over fear of backflipping in general.