This might sound like some sort of rude activity for sports and leisure, but it's a a perfectly acceptable thing to do.
You pick up a caber (a fallen tree), and toss (throw) it as far as you can. The one who tosses it the furthers, wins! In the old days, after McScots unfortunate death, the Scots used to toss the caber to see who would become the new king.
Nowadays, the Scots doesn't need a king to rule, so they toss the caber for fun. It is a common mistake to think that the caber only gets tossed at Highland Games. Caber tossing is a daily activety. Scots just carry their cabers around, and then toss it when they feel like it!
Children use mini cabers... or branches (twigs for infants).
This lovely picture is of me tossing a caber up in the Highlands... I didn't bring my caber that day, but when the urge came to toss the caber, I just picked up a fallen tree, and tossed away!