Observations & having a go at Live Action Role Play games, films in the early 90s and before showed shields only used defensively, often clumsily. This is very different to current film and TV showing combat with such weapons.
Longer medieval shields were flopping a lot as held vertically not giving too much control. In particular, what was noticed was that when striking with the weapon arm, the shield was swung to the back opening the body to strikes. In particular the upper arm of the weapon arm is the most exposed when swinging and an easy target along with your shoulder. Modern fight scenes in movies and TV shows now tend to be far more graphically violent showing shields as a far more offensive weapon, especially using the edge. Bar the issue of weight and encumbrance of a bulky object, this seems to be a better place for shield. Looked at holding kite shields horizontally instead of vertically, this appeared to offer more offensive use.
What I wanted to look at was how to make the shield more of an offensive weapon in the mock combat sport game, much more like seen in film scenes like this one from the film Troy. Note how with the figure of 8-shield used by Achilles (Brad Pitt), the indents are used to hold weapons and catch opponents, as well at the shield edge.
This led to researching alternative shield types with more offensive attributes such as an
Italian lantern shield.
(This is the picture with the gauntlet glove), those with pointed centre boss spikes and blades.