run wild
• grow or develop without restraint or discipline.
• "these horses have been running wild since they were born"
Similar:
grow unchecked,
grow profusely,
run riot,
spread like wildfire,
ramble,
straggle,
run free,
run amok,
get out of control,
cut loose,
be undisciplined,
go on the rampage,
go bush,
raise hell,
go postal,
