Frontlines, sure, but not in the exact front. That was the place for their biotics and heavy hitters. He was a sniper, he preferred to be a nice distance from the oncoming hostiles - when possible. He didn't carry the assault rifles for show, after all. But that's back in his world, where crap makes sense, and the only walking dead are Husks.

On second thought, maybe that doesn't actually make a lot of sense.

His grip is hampered, somewhat, by the crossbow in one hand, but he gets his free hand around one of the nearest corpse's wrists. A simple, rapid twist. It should be pinned in a better position to throw an elbow in its face - or... or the arm could just break off. Right there at the elbow. Garrus looks down at the limb. The corpse looks down at the limb.

He throws it in the corpse's face, and high-tails it in the direction of Claude's voice. When in doubt, distraction, and tactical retreat.

"Got it in sight! I'm with you!"