Crabgrass seems to take a hold when the cooler season lawn grasses go dormant. Probably took a chance to move in when the grass was stressed by the waterslide, too.
I also am battling crabgrass a bit. Trying to hand/shovel weed some, collecting as much seed as I can to prevent next year, and filling those holes with
compost. I will probably seed in a couple weeks (=cooler) so the lawn seed can get established.
I too dislike crabgrass for its aggressiveness tending to kill out lawn grass and short-lived life which leaves bare & dead spots.
Will try corn gluten next spring when the forsythia bloom, then probably again in mid July once the lawn grasses slow down their growth. The mower is set to 4 or 5" too so that should help the lawn grasses compete well too.