This is a common etiquette in Chinese Martial Arts. The etiquette is known "Bao Quan Li 抱拳礼" (literally translated as "Fist Wrapping Rite". You will see this in Chinese Kungfu movie or in chinese martial arts sparring.
The common practice is as follow:
Stand Upright with the body straight. Clench your right fist. Straighten your left palm to have 4 fingers in plane, and your left thumb slightly bend. Wrap your two hands together (the left palm over the right clenched fist). Placed the two hands in front of your chest, but making sure that your two eldows do not come up.
There are philosophical martial arts meaning about this practice: The left palm (with 4 fingers) symbolizes Virtue, Wisdom, Health, Art, which are also called the "4 nurturing elements", symbolizing the spirit of Martial arts. The left thumb is slightly bent to mean that one should not be arrogant or always attempt to be no.1 . The right fist symbolizes rigorous practice. Since the right fist is clenched, it means a form of 'attack' but with the left palm wrapping it, it means "discipline" and 'restraint/control in order not to abuse the martial practice".
Another explanation is that the left hand symbolizes the "5 lakes 五湖" while the right fist clenched symbolzies "4 sea 四海"). When the left hand is placed onto the right hand, it means that "people in the 5 lakes and 4 seas are all brothers" (五湖四海皆兄弟). It's a practice to respect and prevent fightings among the different martial groups in the past.