They ripen somewhat unevenly, with the dark seeds being expelled a few at a time like this
The stems are up to about a metre (3 feet) tall, tough and slightly ridged. There are nodes that look like this - the leaves look like this.
The seeds (which are the thing that make me suspect this is not a true grass and is perhaps a sedge) are about 2 to 3 mmm long and look like this - the middle one has been cut in half, revealing a white, starchy interior.
This is at the damp, lower end of an arable field in southern England.
One of several varieties of Foxtail (Poaceae). At 1 m tall it’s likely Yellow Foxtail which grows somewhat taller than the others. Native to Eurasia, it’s also widespread across North America. It is a true grass, not a sedge.
Looking more closely at the seed head, I’d go with Bristly Foxtai (Setaria verticillata) or something mighty close to it. I’m working from a knowledge of North American weeds, English varieties or sub-species might be somewhat different. Did you notice whether the seedheads would stick to clothing? If they did it’s almost certainly Bristly foxtail… the others, AFAIK have smooth beards.
These were sort of softly fluffy - not bristly or grippy. I did manage to acquire one of the feathery bristles as a splinter, but I think that was just bad luck of the same kind as when a pet hair works its way into a skin pore.
Pretty sure this plant is some species of Setaria. It may not be wild or native - could be a remnant of a previous fodder crop - the maize in these fields is always cut for silage - there are other robust, abundantly-seedy grasses in amongst and around the margins - might even have been planted as some sort of mixture.