Go to the "Reservoir" arena level. At the beginning of the 
match, boost backwards to the point where your AC is almost 
out of bounds (indicated by the red line on your radar). 
Most arena opponents will try to get in behind you to attack. 
Using this trick will cause them to go out of bounds. You may 
take a little damage, but most fights will be over within ten 
seconds. Keep in mind that some opponents will not fall for 
this, but most will.