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