Here is the full list of all 50 Monster Energy Supercross - there are The Official Videogame 4 achievements.
Complete a Main Event in a Custom Track created by another player
Accept the contract of a Team you asked to join
Earn a total of 1,000,000 SX Credits
Get a Holeshot in any game mode
Get a total of 13 Holeshots in any game mode
Win a Main Event with the Event Type option set on "The Real Thing"
Purchase a total of 10 components for your Rider Customization
Complete the Futures chapter in Career Mode
Complete the Rookie chapter in Career Mode
Complete the Pro chapter in Career Mode
Reach the podium in 100 Main Events in any mode
Reach Prestige level 20
Reach Prestige level 60
Reach Prestige level 100
Create a rider with a female body type
Complete all challenges in the Journal
Meet a Contract Objective of an Official Team in Career mode
Complete the entire Skill Tree
Take part in at least 10 Extra Events
Create a rider with a male body type
Pass at least 10 Training Sessions with any result
Complete all the Training Sessions with the maximum result
Ride 100 miles (160 km) in offline Free Roaming in the Compound
Win a Main Event in Anaheim 1 in any game mode
Win a Main Event at St Louis in any game mode
Win a Main Event in Anaheim 2 in any game mode
Win a Main Event in Glendale in any game mode
Win a Main Event in Oakland in any game mode
Win a Main Event in San Diego in any game mode
Win a Main Event at Tampa in any game mode
Win a Main Event in Arlington in any game mode
Win a Main Event in Atlanta in any game mode
Win a Main Event in Daytona Beach in any game mode
Win a Main Event at Salt Lake City R11 in any game mode
Win a Main Event at Salt Lake City R12 in any game mode
Win a Main Event at Salt Lake City R13 in any game mode
Win a Main Event at Salt Lake City R14 in any game mode
Win a Main Event at Salt Lake City R15 in any game mode
Win a Main Event at Salt Lake City R16 in any game mode
Win a Main Event at Salt Lake City R17 in any game mode
Beat a Rival in Career Mode in any race
Complete your first Journal Challenge
Save a custom Bike Setup
Change the colour of the nickname on the suit of your custom rider
Complete an Official Championship of any class in Championship mode
Get a Holeshot and victory in the same Main Event in any mode
Complete a total of at least 100 scrubs
Beat the time of the Ghost of another player in Time Attack mode
Complete at least two SX Challenges of the SX Profile
Complete a lap with the Dynamic Flow Aid activated