Logrolling is an aquatic sport in which two people balance on either end of a log lying flat in the water, and one of the competitors starts to walk, causing the log to roll. The other competitor must keep up with the rolling log, or fall off, ending the round. This sport originates in North America, especially in the Pacific Northwest of the United States and Canada, although it has spread to an international level, thanks to the work of advocacy organizations.
As you might surmise from the fact that a log is involved, logrolling originated in the lumber community. Many logging communities took advantage of local rivers to transport logs for free, felling trees, trimming them, and then rolling them into the river and allowing them to float downstream to the mill pond, at which point they could be hauled out and processed. Periodically, it would be necessary for people to walk on the logs to manipulate their arrangement in the mill pond, and this evolved into a game in which lumberjacks would challenge each other to keep up on a rolling log.
This sport is also known as birling. Historically, loggers participated on any logs which happened to be available, adding to the challenge and potential danger. In fact, logrolling could be quite perilous in a crowded millpond, as loggers ran the risk of being crushed between other logs in the pond if they fell. Modern logrolling uses standardized logs which have been trimmed to size, and some competitions even involve synthetic logs.
The goal behind standardization is to make the sport fair for all competitors, by ensuring that no one gains an unfair advantage with an especially well-balanced or favorably-textured log. Standardization also makes the sport safer than it might be otherwise. Competition logs are typically painted with bright stripes which make them easy to visualize in the water, and some include carpet or other textured materials to make it easier to grip the log.
For the most part, competitive logrolling is dominated by men, as are timbersports in general. However, women can and do compete, and some of the best logrollers in the world are women. The American Midwest in particular seems to breed strong female athletes, and in some cases multiple generations compete together. As with other timbersports, logrolling celebrates aspects of the timber industry which would otherwise be lost, as few mills use rivers and millponds as a method of handling timber today, and logrolling on the job would be considered a serious safety violation.