NHL teams play to the score, especially in the playoffs. Late in the game, the leading team will take fewer chances and try to choke off the game, while the losing team will press for an equalizer and usually put as many pucks on net as they can.
The Detroit-Columbus series was an interesting showcase for how teams play based on the score, as Columbus didn't spend a single second of the series in the lead. That makes it easy to analyze the numbers, since we don't have to go through and remove any time that the Blue Jackets spent in the lead.
One thing that was striking in both my numbers and those at Hockey Numbers was that the expected goals totals for the Blue Jackets were very close to that of the Red Wings. This seems to indicate that the play was much closer than what observers were reporting. Often I tend to side with numerical evidence over eyewitness accounts, but on this one I think it is pretty clear that the eyeballs were seeing something that the math wasn't taking into account, namely that the Detroit Red Wings playing to win.
It has been well demonstrated that trailing teams tend to shoot more, and that teams with a large lead tend to shut it down somewhat to help preserve their lead late in games. Therefore, we would expect that Columbus' shot totals and expected goal totals to be overstated, and for Detroit's numbers to be understated. This turns out to be the case.
Let's break it down further. Detroit had a large outshooting edge in the first 2 periods (104-73), and shots were essentially even in the third (37-36). That is the kind of result we would expect to see for a talented team like the Red Wings against an overmatched opponent - take control early, score a few goals, and then kill the clock.
As I observed in my last post, point shots may be somewhat of an indicator of possession. Over the first two periods, Detroit had a 19-8 edge in point shots. In the third period, they took just 7 to Columbus' 5. That likely indicates that Detroit spent much of the first two periods in Columbus' zone, allowing their defencemen to get set up and fire at the net, but gave up that possession advantage in the final period.
Perimeter shots are similar in that they indicate possession, although they are more up to the shooter's discretion since they come from less well-defended areas and are therefore probably more likely to end up on net. In first periods throughout the series Detroit threw everything at the net, with 25 perimeter shots on Mason. In the second that dropped to 11, and in the third just 14. Osgood faced few perimeter shots the whole way, just 7 in the first and 10 in each of the second and third periods.
I would have expected Columbus to take more long shots when trailing late. I'm pretty sure that the Red Wings would show an increased perimeter shot rate when trailing late in games. Maybe the Red Wings' forwards were doing a great job of preventing or blocking shots. Or perhaps the Blue Jackets have different offensive tactics, and prefer to try to generate more high-quality scoring chances. They were actually fairly successful at getting high-quality scoring chances against the Red Wings, so if that's the case it might not have been a bad strategy, Osgood just managed to hold up better than expected in net.
In the third period Detroit seemed to be trying extra hard to limit those high-quality chances, and they were pretty successful in doing so. In the first two periods combined, Osgood faced 20 shots from the crease area while Mason faced 13. In the third periods, Osgood faced just 3 while Mason only had to deal with 2. This shows the tradeoff for the leading team: They reduce their chances to score as well as the opposition's. When up a goal or two in the third, however, this appears to be a favourable strategy.
Perhaps the biggest sign that Detroit wasn't trying as hard to score was that in the third period they very clearly stopped trying to shoot high. In the first two periods, 30% of the shots on Mason were high. In the third, just 17% were high. Osgood's numbers went from 14% to 11%.
These numbers show that both goalies were facing much easier shots in the third period. Taking into account both shot location and shot height, my estimate is that over the first two periods the expected save percentages for the two goalies were .915 for Osgood and .929 for Mason. In the third, those numbers rose to .926 and .945 respectively (.921 was the average).
Four games is a small sample size, so some of these results may have been random chance. However, they all seem to support playing to the score effects that have been observed in larger samples, so there is likely something significant there.
In summary, the shot charts make it look like Detroit and Columbus played a fairly close series, and that Mason played poorly while Osgood played well. The underlying numbers, however, suggest that the Red Wings were clearly the better team, and shut down their offence when they had the game in hand. If Columbus was able to keep the games closer, or if the Red Wings had decided to keep trying to score all the way up to the final whistle, the expected goals would have been much more tilted in favour of the defending champions.