I agree to aim low Quaffer but the feet are maybe too low, if you're new to support aim hip-level but after you've got some experience you should be aiming at the stomach to chest and pulling back on the mouse after the first shot.
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Anything less than 40 hit points why not hop into fire and prep your medic at 24HP?
If you're charging into the Kalt wheelhouse when the enemy has a bridge, throw a grenade high into the room first. If you hear someone take damage ("Ahh"), throw another one and immediately run into the room. They'll be dazed or dead or retreating.
A peeking opponent will have a shot advantage over a player in a fixed position if they know where you are. Keep this in mind, offensive snipers always have a slight advantage over camping snipers or MGs!
Never round a corner that an MG or sniper's watching with anything less than a sprint or shaky strafe moves. At range, don't give them an easy target, if it's just a sniper and he misses, shoot back! You have at least two seconds and you might get lucky, and then get moving again! Do not crouch or prone against a sniper in cover trying to get lucky, that's silly and you will die. Move, move, move.
Don't be so eager to throw grenades in close combat. Experienced and aggressive players will sniff out your desire to throw one and they'll find you before you can toss it. Instead, be aggressive and challenging.
If you're cooking a grenade, move around, strafe back and forth or whatever but make yourself a hard target to hit, you're a sitting duck while that thing cooks!
If you're flanking the enemy team on the Kalt bridge and they're holding the bridge, either run below the bridge or on the far side of the concrete sides of it so you avoid the capture area. Attentive players will notice that there was an enemy on the bridge behind them and they'll snap around for a shot. If you've ever flanked the bridge and seen someone snap 90 degrees to blast you, this is why.
You CAN catch grenades in mid-air and you should! If you're on a capture point and a grenade lands at your feat you're really better off picking it up and either throwing it or just dying. You don't lose any points in HLXStats for a suicide and chances are they would have killed you anyway with another grenade. Just don't run away from a grenade that lands at an MG or sniper's feet, if you're close enough, pick it up and they'll respect you as long as you play there.
Grenades are not always killing weapons, sometimes they can be used to distract enemies. Arc a high-flying grenade in the air and towards a gaggle of players and then immediately run out to start shooting. Players are easily distracted and they'll stare at that grenade and go (oooh pretty) before they realize you're exposed and already taking aim.
good stuff