BF42 has a static sky so at the beginning of a match (and in some, throughout) you can quickly jump into a tank or artillery and destroy enemy assest before they even move them (namely planes). On Battleaxe, the Allies can destroy both enemy planes before takeoff and on MG Axis can take out one of the planes at the beginning. From playing in TWL matches a long time ago with this game I can speak from experience (I can also tell you other maps that it can be done on).
Basically, the match starts and the closest one to the tank or whatever jumps in, aims the cannon at a certain spot in the sky, and shoots. It's a rotten tactic but in the competitive world without a way to monitor it it's going to happen.
I'll give you an example that I used in a match before (if you can't beat them you have to join them, right?): In Battle of the Bulge on the Allied side there's a flag that spawns an M10, just south of the Axis base. I could actually hop into that, turn the gun to the left, and align it with a certain spot on the camouflage mesh it was under to destroy a PanzerIV on one shot at the wheels, all within 5 seconds. No, it's not aiming at the sky but you could actually do that trick with the artillery that spawns at the main Allied base. Someone jumps in the artillery and turns it just right so that you can hit the east bridge from that base without the need of a scout. (I'm not going to give hints on how to do it on the maps listed for the tournament) It's a tactic that is legal in most competitive ladders, the reason why I joined the 3FL since it had a gentlemen's agreement to play the way the developers intended the game to be played.
Anyways, that's pixel-aiming.
I thought this issue was addressed at the first 100-man LAN?