new bool:g_bLadder[MAXPLAYERS+1];

public OnClientPutInServer(client) g_bLadder[client] = false;

public Action:OnPlayerRunCmd(client, &buttons, &impulse, Float:vel[3], Float:angles[3], &weapon) 
{ 
	if(!g_bLadder[client] && GetEntityMoveType(client) & MOVETYPE_LADDER)
	{       
		g_bLadder[client] = true;
		PrintToChatAll("Игрок %N залез на лестницу", client);
	} 
	else if(g_bLadder[client] && !(GetEntityMoveType(client) & MOVETYPE_LADDER))
	{
		g_bLadder[client] = false;
		PrintToChatAll("Игрок %N слез с лестницы", client);
	}
	return Plugin_Continue; 
}