Definition of put up one's guard in US English:

put up one's guard

phrase

  • Adopt a defensive posture.

    • ‘I put up my guard, but there wasn't anything wrong with playing along!’
    • ‘There was a little desperation in his voice and it immediately made her put up her guard.’
    • ‘The group put up their guard and Shu was put in the centre of their tightly knit circle to keep him from direct harm.’
    • ‘As soon as he enters the room, the old woman begins to be suspicious and puts up her guard.’
    • ‘At the mention of her husband she immediately put up her guard.’
    • ‘It was the times when he reminded her of the Tyler she knew in high school that made her put up her guard.’