To become difficult to control:
It was the end of term and the children were getting a little out of hand.
If a situation or person gets out of hand, they become impossible to control any longer
The demonstration was getting out of hand.
From Longman Dictionary of Contemporary English
Examples from the Corpus
Get out of hand
• The costs have continued to increase, and now seem to be getting out of hand.
• But has the Fed failed to prevent the imbalances created by the recent boom from getting out of hand?
• My mum used to sit nearby and make sure nothing got out of hand.
• We let ourselves get out of hand.
• It was a practical joke that got a little out of hand.
• Pull or spray garden weeds before they get out of hand.
• Hundreds of police were poised to intervene if things got out of hand, but they did not.
• Police were called in when the situation began to get out of hand.
• Things started to get out of hand.
• This was getting out of hand.
• But eventually it became clear that things were getting out of hand.