To undergo a weigh-in.
His trailer weighed in lighter than it should have. He might have a leak.
To subject to a weigh-in.
They had to weigh him in at the loading dock.
(with "at") To weigh.
He weighs in at upwards of 250 pounds.
To bring in one's weight, metaphorically speaking, to bear on an issue; frequently construed with on or with.
Everyone spoke freely, until the boss weighed in.