Fun fact: 9/10 users with no linked gamertag are better than you at Halo. That doesn't necessarily mean that I am; but it does mean there's a pretty solid chance.
'At a dangerous time' isn't the point. Use your eyes as you play. Learn the layout of the map. It takes perhaps two games- or half an hour in forge- to memorise the general layout and features of a map, and whereabouts each team will spawn. If you're doinitright, you shouldn't find yourself in situations where you've got your back to a wall unless you've got team support. Know your surroundings and think about what you're doing and it simply won't happen.