If you want something really basic then this would be it:
PHP Code:
#include <sourcemod>
#pragma semicolon 1
public Action:OnPlayerRunCmd(client, &buttons, &impulse, Float:vel[3], Float:angles[3], &weapon)
{
if (IsPlayerAlive(client))
{
if (buttons & IN_JUMP)
{
if (!(GetEntityFlags(client) & FL_ONGROUND))
{
buttons &= ~IN_JUMP;
}
}
}
return Plugin_Continue;
}