Something

AHL_DIVE_DIRECTION_LEFT = "left"
AHL_DIVE_DIRECTION_RIGHT = "right"
AHL_DIVE_DIRECTION_FORWARD = "forward"
AHL_DIVE_DIRECTION_BACKWARD = "backward"

AHL_DIVE_TIME = 0.5
AHL_DIVE_MOMENTUM = 300.0
AHL_DIVE_ZFACTOR = 200.0
AHL_DIVE_ROLL_TIME = 1.5
AHL_DIVE_ROLL_SPEED = 50

AHL_DEBUG_ENABLED = true

function dive(pl, command, args)
   if (pl.Diving || pl.Rolling) then return end
   
   if (pl:KeyDown(IN_MOVELEFT)) then
      pl.DiveDirection = AHL_DIVE_DIRECTION_LEFT
   elseif (pl:KeyDown(IN_MOVERIGHT)) then
      pl.DiveDirection = AHL_DIVE_DIRECTION_RIGHT
   elseif (pl:KeyDown(IN_BACK)) then
      pl.DiveDirection = AHL_DIVE_DIRECTION_BACKWARD
   elseif (pl:KeyDown(IN_FORWARD)) then
      pl.DiveDirection = AHL_DIVE_DIRECTION_FORWARD
   else
      return
   end
   
   debugLog(pl, "Dive type '" .. pl.DiveDirection .. "' detected")
   
   debugLog(pl, "Initiating dive, initial velocity = " .. tostring(pl:GetVelocity():Normalize())) 
   pl:SetVelocity(pl:GetVelocity():Normalize() * AHL_DIVE_MOMENTUM + Vector(0, 0, AHL_DIVE_ZFACTOR))
     
   pl.Diving = true
   pl.DiveCompleted = false;
   timer.Simple(AHL_DIVE_TIME, completeDive, pl)
end

function completeDive(pl) 
   pl.DiveCompleted = true 
   debugLog(pl, "Dive completed")
end

function completeRoll(pl)
   pl.Rolling = false;
   debugLog(pl, "Roll completed")
end

function onThinkDive()
   for k, pl in pairs(player.GetAll()) do
      if (pl.Diving && pl.DiveCompleted && pl:IsOnGround()) then
         pl.Diving = false
         pl.Rolling = true
         debugLog(pl, "Initiating roll")
         timer.Simple(AHL_DIVE_ROLL_TIME, completeRoll, pl)
      end
   end
end

function onThinkRoll()
   for k, pl in pairs(player.GetAll()) do
      if (pl.Rolling) then
         if (pl.DiveDirection == AHL_DIVE_DIRECTION_RIGHT) then
            pl:SetVelocity(pl:GetAngles():Right() * AHL_DIVE_ROLL_SPEED)
         elseif (pl.DiveDirection == AHL_DIVE_DIRECTION_LEFT) then
            pl:SetVelocity(pl:GetAngles():Left() * AHL_DIVE_ROLL_SPEED)
         end
      end
   end
end

function debugLog(pl, msg)
   if (AHL_DEBUG_ENABLED) then
      pl:PrintMessage(HUD_PRINTTALK, msg)
   end
end

concommand.Add("dive", dive) 
hook.Add("Think", "ahl_think_dive", onThinkDive)
hook.Add("Think", "ahl_think_roll", onThinkRoll)