going into one's shell

Verb

go into one's shell (third-person singular simple present goes into one's shell, present participle going into one's shell, simple past went into one's shell, past participle gone into one's shell)

1. (idiomatic) To act defensively.
   • Instead of gathering the ball, De Gea poked it away with his foot and Streller was able to place a powerful half-volley into the net.
     United went into their shells and it was not until the 29th minute that they mustered a response - one from which they should have equalised.2011 December 7, David Ornstein, “FC Basel 2 - 1 Man Utd”, in BBC Sport