From what I've heard, the game uses client-side hit detection, so if it looks like you hit someone on your screen, then the server trusts that you actually hit them. If one player has a high ping, they could pop out of cover and shoot someone before the other player even has a chance to see them. They might also be able to get multiple shots off against a player before the target even has a chance to hear the first one and duck behind cover. To the low-ping player getting shot at, it will appear to them that they got shot after taking cover, but to the high ping player, they would have been taking multiple shots while the other player was still exposed. In short, it sounds like the game might have poor netcode.