It's literally attacking with a higher bridge, to avoid all fight (and skill) land on the egg and then mine the egg,and it costs a ton of iron to stop it before you lose your egg, Fun fact, some people start rushing mid while being air attacked, so when they're almost at 80% of building the midbridge, the attackers will have mined the egg and killed them already, so its basically suicide , but instead of one member it is suicide for the entire team.