Here is the full list of all 50 Knockout City achievements.
Win 10 matches while grouped with a Friend
Win a match while having a Legendary Outfit equipped
Win a match while having 5 or more Legendary accessories equipped
In the Hideout, tackle the T.A.R.G.E.T. Dummy off the roof
Win 5 matches while grouped with a Crewmate
Throw a Caged player off the map
Win a match while having Legendary Gloves equipped
Complete 5 Season Contracts
Earn 50,000 XP
Earn 100,000 XP
Earn 250,000 XP
Play 30 matches while grouped with a Friend
Use 5 Energy Drinks
Play 100 matches
Score 1000 KOs
Be the MVP of a three or four player team 5 times
Win 30 matches
Catch 1000 dodgeballs
Score 1000 KO Assists
Score 100 KO Finishes with Ultimate Throws
Travel 100km in ballform
Win 10 rounds with five times the opponent's score
Win a match without being KO'd
Score 10 KOs without being KO'd
Win a match without throwing a single dodgeball - Passing is allowed!
Win matches with 10 unique Outfits
Win a match while having an Uncommon (or rarer) accessory equipped in each slot
Win matches with each Style of an Outfit
Win matches with 20 Outfit and/or Glove Styles
Win a match while having Legendary Glasses equipped
Win a match while having a Legendary Glider equipped
Complete 100 Daily Contracts
Complete 30 Crew Contracts
Complete 5 Event Contracts
Complete the first 5 Training Levels
Complete 100 Contracts
KO two opponents with a single Bomb ball
Score 3 Hits with a Multi Ball in quick succession
Catch a Sniper Shot
Be airborne for 30 seconds straight while holding a Moon Ball
In Rooftop Rumble, KO Finish 3 players without leaving the bridge
In Concussion Yard, KO Finish an opponent while riding the Wrecking Ball
In Knockout Roundabout, KO Finish an opponent while riding a car
In Galaxy Burger, KO Finish an opponent with a trash chute
In Back Alley Brawl, Avoid a thrown dodgeball by entering a Tube
In Concussion Yard, ride the wrecking ball for 15 seconds straight
In Rooftop Rumble, glide from the Bandstand to the Gardens
In Knockout Roundabout, ride a car all the way around
In Galaxy Burger, fall through a trash chute
In Back Alley Brawl, throw a ticking Bomb Ball into a Tube