// These defines are for client button presses.  
#define IN_ATTACK  (1 << 0)  
#define IN_JUMP   (1 << 1)  
#define IN_DUCK   (1 << 2)  
#define IN_FORWARD  (1 << 3)  
#define IN_BACK   (1 << 4)  
#define IN_USE   (1 << 5)  
#define IN_CANCEL  (1 << 6)  
#define IN_LEFT   (1 << 7)  
#define IN_RIGHT  (1 << 8)  
#define IN_MOVELEFT  (1 << 9)  
#define IN_MOVERIGHT  (1 << 10)  
#define IN_ATTACK2  (1 << 11)  
#define IN_RUN   (1 << 12)  
#define IN_RELOAD  (1 << 13)  
#define IN_ALT1   (1 << 14)  
#define IN_ALT2   (1 << 15)  
#define IN_SCORE  (1 << 16)    // Used by client.dll for when scoreboard is held down  
#define IN_SPEED  (1 << 17)    // Player is holding the speed key  
#define IN_WALK   (1 << 18)    // Player holding walk key  
#define IN_ZOOM   (1 << 19)    // Zoom key for HUD zoom  
#define IN_WEAPON1  (1 << 20)    // weapon defines these bits  
#define IN_WEAPON2  (1 << 21)    // weapon defines these bits  
#define IN_BULLRUSH  (1 << 22)  
#define IN_GRENADE1  (1 << 23)    // grenade 1  
#define IN_GRENADE2  (1 << 24)    // grenade 2

public Action:OnPlayerRunCmd(client, &buttons, &impulse, Float:vel[3], Float:angles[3], &weapon)
{
   if (buttons & IN_ATTACK2)
   {
     new String:classname[64];
     GetClientWeapon(client, classname, sizeof(classname));
     if (StrEqual(classname, "weapon_knife"))
     buttons &= ~IN_ATTACK2;
   }
}