I think it was more complicated than that. Glynn's signalling perhaps was momentarily inconsistent, because Sano inexplicably started pulling up while halfway between second and third. If Glynn was windmilling to indicate a dash for home was still possible, then had to switch to a stop sign a millisecond later than he could have, confusion may have entered in, causing a further hesitation on Sano's part and then a belated decision to go for it. As the final outcome proved, the stop sign never was absolutely necessary in terms of being able to make it (maybe, with only 1 out, caution still was advisable), and Sano going all out once past second base would have scored easily. Not good, and you'd like for all concerned to process the emerging information just a little better, but perhaps not simply a willful ignoring of a stop sign. The video unfortunately doesn't show enough of Glynn, but at the 0:53 mark you see the left hand up for Stop and the right arm pointing Home. I'm trying to make sense of that. Blyleven's saying Glynn is pointing to the cutoff man, but maybe that's too complicated a signal for the situation. https://mediadownloads.mlb.com/mlbam/mp4/2018/04/05/1906794883/1522886995189/asset_1800K.mp4