Beer in airlock

Hello!
So for my first brew attempt I added half the water, boiled, to the fermentor at the beginning then added the wart and tossed it back and forth several times as suggested by the Palmer book I'm using. I ended up with too much and the fermenter nearly exploded! Beer out the airlock, lid, bulging top and all. Scary! Put it under a table to protect the walls/ceiling in my tiki room. Racked it Sunday and seemed all good. This time I added bottled water at the end and hit the 5 gal mark. On day two, the airlock turned yellow. No biggie like the first time but is this normal? Seems like a lot of bubbles are caused by the tossing back and forth of the wart/water mix which eats some of the head space. Do most folks aerate this way? Is it normal to have some beer come into the airlock during fermentation? I'm not worried about the batch, just thinking about the future and my routine. Thanks. Great forum.

It's normal if you have a very active ferment and not much headspace.

If you see krausen (the yeasty foam that forms during the active phase of fermentation) in your airlock, you can rig up a blow-off tube, which should keep the beer from shooting your airlock/fermenter lid across the room.