Here is the full list of all 27 Riskers achievements.
Complete all side missions
Kill Thomas
Kill 50 people with a baseball bat
Kill 10 enemies with a chair
Kill an armed enemy unarmed
Complete all race challenges
Complete all shizo challenges
Kill Dino
Unlock brass knuckles
Kill 100 cops
Run over 50 people with a police car
Achieve the fastest car speed
Steal 100 cars
Kill 2 people with a single sniper shot
Kill 4 or more people with a single grenade explosion
Punch and run, have 3 or more people after you
Complete all time attack challenges
Complete all challenges
Kill Shuba
Complete the main story missions
Complete the game 100%
Find the inflatable duck
Find all hidden posters
Destroy 100 cars
Complete all achievements
Smash a window with a chair
Kill an enemy while jumping/sliding over an object