Your dad raises foster kids (you, your little brother, and one of your half-brothers were adopted by him a few years ago), and a few weeks ago, Dad took in four new kids, 5, 7, 12, and 15. When he took them in, he cleared all your chore strikes to help avoid getting in trouble, while the new kids were still 'working up' to the rules (Dad doesn't spank for the first several weeks, so the kids have a chance to learn the rules and expectations).
Admittedly, chores have always been a problem for you. You mean to do them, but there's always so much else to do, and sometimes it's hard to remember to do them on time or the way dad wants. And since you don't get in trouble for skipping one occasionally, it's easy enough to let them slip by occasionally. The problem is, when you're out of time, and one slips by on accident. Then Dad makes sure you pay the price.
Last Saturday, you got your second strike. You should have done a work off then, but it was a really nice weekend, and you kind of forgot about it. Tonight, it's your turn to load the dishwasher, but you get a little distracted, and you don't do it right, don't turn it on, and don't wash out the sink. Dad would probably have let you slide on one of those, and maybe given you a final warning on two, but all three?
Now Dad's giving you a choice. He normally uses his hand for chores, which still hurts, but doesn't burn as long. However, if he does that, it would normally be right here, and then you'll have to re-do your chore with your bottom bare, to make sure you get it done right. Your other option is to go to his room, where no one will know you were spanked, but he'll use the paddle, which hurts a bit more than his hand, but that leaves you sore a lot longer.