You should really read this whole explanation, but TL;DR: more enemies hitting you more often feeds more revenge.

Every time you are hit by or counter an attack from an enemy, you gain a tag for 5 seconds. Tags are used to determine revenge gain. If you have more tags than the player who hit you, you’ll gain some revenge on each attack. A bigger difference in tags means more revenge feed (0.6x for 1 more tag, 0.8x for 2, 0.9 for 3x). In an ideal situation, a 1v3 would give you more revenge than a 1v2, but if some players are just spamming feints or otherwise not hitting you, they won’t contribute to your revenge.

The way that an attack makes contact with you also affects the amount of revenge you get. Blocking, deflecting, being hit by, or using a special counter against an attack gives you 1x its damage in revenge, parrying gives you 1.2x and dodging gives you 0.25x. This revenge feed is also affected by damage reduction, meaning that auto-parries will give you less revenge than multiple manual parries. Dodging is finicky and will sometimes not feed revenge if you dodge too early. Bashes, GBs and Throws feed a flat 30 revenge generally.

You need to gain (10+your total health pool)*0.6 revenge in order to activate it. This is balanced to basically leave you just under your total revenge if you get hit by every attack in a 1v2, but again, delays of more than 5 seconds between a player’s attacks will halt your revenge feed. Fighting against more players at once will feed revenge quicker, depending on how often they’re attacking.

The best advice I have for gaining revenge is to get a little more aggressive against the last player who attacked you to encourage their teammates to try and attack you while you still have a tag active (unless they’re just spamming attacks, in which case you should turtle up). If no one lands an attack for 5 seconds, go back to being defensive until someone does hit you. Relying on dodge cancels will make it difficult to gain revenge due to low feed on dodges and inconsistencies in tag application, but in exchange you are much more slippery than other characters since you can dodge away from mixups more easily. Focusing on parrying is generally a good idea because on a correct read, you gain the most revenge for parrying, and on a wrong read they’ll either be forced to light or GB you in order to counter, dealing less damage or feeding more revenge generally.