Bug Off

From Halopedia, the Halo wiki

The Bug Off medal is awarded in the Halo: Spartan Assault Flood missions for using the Overshield to prevent infection. It is represented by the Overshield symbol on a blue shield.

An infection occurs when a large Pod infector latches on to the player's back. Once this occurs, the player is unable to use their armor ability. To earn this medal the player must activate their Overshield then allow a large infection form to touch them; this will cause the infection form to pop rather than latch on, and the player will receive the medal.