Interesting. Looking at that YouTube video for a 'somersault', the first thing I thought was "but that's a 'forward roll', surely?".
The OALD definition for 'somersault' is:
noun a movement in which sb turns over completely, with their feet over their head, on the ground or in the air: to do / turn a somersault * He turned back somersaults. * (figurative) Her heart did a complete somersault when she saw him.
verb [v, usually + adv. / prep.] to turn over completely in the air: The car hit the kerb and somersaulted into the air.
This surprised me, because I always think of somersaults as being flips through the air and forward rolls as being head and hands on the ground like in the video. I found this forum discussing the term 'somersault' which may be of some interest, particularly with the comments by the British speaker (Mike). If somebody asked me if I could do a 'forward roll' my answer would be 'yes'. If the same person asked me if I could do a somersault, I would give them a resounding 'no!'