A few decades ago, tai chi was practised mostly as a combat martial art and was more commonly called tai chi chuen. Chuen means fist and denotes combat. Nowadays there are still some students learning tai chi for combat purpose. Like any activities, promoters wanting more students must preach the efficacies of their arts. Combat tai chi not exempted. What better credentials nowadays then full contact tournaments? The rules are clear, the winner will be clear winner!
A few decades ago, tai chi masters did participate in combat sports in Hong Kong, specifically tournaments between different styles of kung fu, and with protective head (and sometimes also body) gears. Participants treated such fights seriously because the winners would have a golden opportunity to promote their arts. Some tai chi masters did take part in such tournaments and as natural law would have it so they won some tournaments (and losing some which nobody would publicize). To put things into perspective, that was the time before Muay Thai fighters arrived.
Nowadays in Hong Kong and in the West, we can hardly see tai chi masters stepping into the ring with a seasoned Muay Thai fighter for a stand up fight. It is not going to be good for publicity, if a tai chi academy's main student source is from those young people who love combat. Fortunately, for most tai chi academies, most (if not all) students who come to learn tai chi simply do not like combat. Health, body building and spirituality are their key learning objectives.
It does not seems to be the case in mainland China. Recently I came across a video in Youtube featuring a fight (under Muay Thai rule!) between a Chen-style tai chi master and a Muay Thai fighter. Wow! That is exciting. The event, according to the description of the video, was held in the home town of Chen-style tai chi and was organized by the local tai chi association, apparently with the objective of promoting Chen-style tai chi as an effective fighting art. And the tournament was held last year between five Chen-style tai chi fighters and five Muay Thai fighters. As things went its natural path, the result was three to two in favour of the Chinese fighters. Everybody was happy, including the Thai fighters who lost their fights (and we can answer the question: Who was running the show). Here is the video of one of the fights. A case study for the marketing of martial arts.