Mars is how you go after things: drive, anger, desire and the way you fight. In Scorpio, it is in its own sign, which means it has full permission to do exactly what it does. Scorpio is a fixed water sign, ruled by Pluto in modern astrology and traditionally by Mars itself. When Mars sits here in a birth chart, the drive has nowhere to leak out sideways. You want all the way, there is no casual pursuit, no clean exit, and you remember exactly what was done to you.
I see this placement a lot on the charts that come through Spisce, and what strikes me every time is how concentrated it is. Other Mars placements spread their focus across several interests at once. Mars in Scorpio picks one thing and stays.