Could you explain this a bit more? To me the change in guard in sport vs bareknuckle fighting seems to have been the result of the large surface area of boxing gloves which allow for different blocking strategies
I agree, its a huge area of discussion and JIMHO, but theres also clinching and clearing of limbs , the ability to grab and strike , the removal of throws etc .
Also the establishment of lines of entry, while most look on covers as defence the are also the line of entry , the whole reason being you cannot occupy the same line at the same time, therefore he who controls the line controls the entry. wearing pillows and outlawing these strategys takes away the advantage of extended guards.
in a compound assault , with intent you lack the ability to use the timing and distancing , seen in sport and mutual confrontation , the element of surprise the ability to bridge and smother and grapple and overwhelm with dirty tactics and cqb renders these skills useless beyond the initial entry.
keeping your hands out also keeps the opponent from clinching you , and we establish the fence(geoff thompson) or the spear (Tony Blaur) this stuff is not new but it is so important , it also necessitates moving in on the attack , attacking defending and moving as one , a counter ambush skillset over a sporting skillset .
but covering the angles(lines of force) controlling the entry you establish the three main factors IMHO of a counter ambush
getting over the advantage line fast , and not having to receive the force at its strongest point.