To begin with, let's have a look at his career record, using TPAK. We have several missing seasons here. In 1910 he played junior-level hockey in the OHA, at least before he was suspended for unsportsmanlike conduct in February of that year. He was in California during the 1911 hockey season, and spent the 1912 season playing for Cleveland in the USAHA, for which statistics are not currently available. After his playing career ended in 1915, McGiffin served in the US Army Air Service during World War I, and died in an airplane accident in Texas, in 1918.
As you can see, he was a pretty marginal player at the NHA level (and in the amateur game), however a large part of this is due to the penalties he took. He loses 45% of his value as a player on the ice due to the cost to his team of being a man down so very often. For the three seasons McGiffin played in the NHA, from 1913 to 1915, the "top" (actually bottom) three penalty rates (per 60 minutes of ice time) all belong to him:
No one comes close to his level of rule-breaking. McGiffin was at least 46% ahead of the second-ranked player on a per-minute basis every season. He was always in the top two in total penalty minutes (leading in 1914), despite usually being a substitute player. And this isn't an artifact of him being careless, or being prone to being in the wrong place at the wrong time. He was in fact noted as a very violent player in his day:
Minnie McGiffin got into the game every now and again and managed to distinguish himself with the usual line of rough work. In the first period he had only been on a minute or so when he chopped [Hamby] Shore and went off. In the second he started the procession to the penalty bench by crashing into [Art] Ross who at once retaliated...McGiffin then replaced [Jack] Walker and knocked [Jack] Darragh flat with a glaring foul. He was given another major. Later he came back to use the butt end of his stick on [Leth] Graham, knocking the youngster cold. (Montreal Daily Mail, 11 Jan 1915)
According to the official list of penalties Minnie McGiffin is the bad man of pro hockey. However, local fans don't think so. They blame the long list to the officials. A leather-lunged rooter at the Arena Saturday night voiced the feeling of the bleachers when the Torontos made a change in the last period: “Blow your whistle, Umps, Minnie's on the ice. (Toronto World, 1 Feb 1915)
Much like many of today's fans, McGiffin's supporters backed him because he was his own team, while at the same time deriding opposing players for their violent tendencies. But there's a good argument to be made that McGiffin was hockey's first real thug. We'll look at the history of thugs in major hockey next time.