Posted: 25/06/2017 at 12:06
Those are suckers of something ............ I think they may be from a Robinia pseudoacacia 'Frisia' .... notorious for suckering. It may be some distance away or it may have been felled and the roots have been stimulated by the felling to start producing suckers.
I would get some SBK brushwood killer and apply it carefully according to the instructions, masking off any other plants around the suckers. SBK only affects broad leaved weeds so it shouldn't damage your grass.
You may have to do this for several growing seasons until the underground root system capitulates.