US president Donald Trump's criticism of American football players who kneel during the national anthem has sparked a mass increase in such protests around the NFL, as about 200 players sat, knelt or raised their fists in defiance.

With the NFL play-offs kicking off this weekend, attention will be divided between three star rookies and one retiring veteran in the most wide-open football post-season in recent years.

IN just his first year as an NFL coach, Jim Harbaugh has brought his San Francisco 49ers to the brink of a Super Bowl appearance.