to bite into (e.g. rope into skin); to cut into; to dig into (e.g. of fingernails)
to eat into; to encroach; to make inroads; to penetrate (e.g. a market); to break into (e.g. first place); to erode; to cut into (e.g. time, savings)
to be wedged (i.e. underwear pulled from the back, driving it between the buttocks)
ベルトが腰に食い込んでいる。
The belt is digging into my waist.
睡眠時間に食い込んでしまう。
It's eating into my sleep time.
競争相手の市場に食い込んだ。
We cut into the competitor's market.