expression, ichidan verb
hoop a barrel; put a hoop on; bind with hoops
Literal meaning: to fit a metal or bamboo hoop around a barrel or tub to hold the staves together. The expression is also used figuratively for tightening discipline or control.
職人が桶に箍を嵌めている。
The craftsman is hooping the barrel.
あのチームは最近緩んでいるから、監督
That team has been slacking off lately, so the coach needs to tighten the reins.