FIELD GUIDE

Hot and cold are only meaningful against a player’s own rate

A list of the league’s top scorers over the last two weeks is mostly a list of the league’s top scorers. That is not a trend, it is a ranking, and it tells a manager nothing he did not already know. The question a waiver decision actually turns on is different: is this player doing more than he usually does, and by enough that it might not be luck? A fourth-line winger with four goals in six games is news; a first-line centre with four goals in six games is a Tuesday.

This page measures every player against himself. For each category your league counts it takes his per-game rate over the window and compares it with his own season rate, scaled by how much his games normally vary, so the figure in each cell says how unusual the stretch is for him rather than how good he is. Add the cells up over your categories and you have his heat.

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How the z is calculated

Every night our game-log job rebuilds each player’s per-game record for the season and cuts three windows from the end of it: the last 7, 14 and 30 game days, where a game day is a date on which the league played at all. Windows are counted in game days rather than calendar days so that the holiday pause and the all-star break never empty a window, and so that before the season opens the page can show the last game days of last season honestly rather than showing nothing. For each category the window’s per-game rate is compared with the player’s season rate, and the difference is divided by the standard error of a stretch of that many games drawn from his own season, which is his per-game spread over the square root of the games in the window. A z of +2 means a stretch this good happens to him about one time in forty by chance; a z of -2 the reverse. A lower-is-better category, goals-against average or penalty minutes, is turned so that positive always means hot. The season rate is this season’s once a player has ten games in it and last season’s until then, because in October a player’s own rate is last year’s and a comparison against five games would be noise measured against noise.

Reading the table

Each category cell shows two figures: the per-game rate over the window on top and the z underneath, with the cell tinted by the z so the eye finds where a player is running above or below himself. The heat at the end of the row is the sum of the z over the categories in play on his side, skater categories for a skater and goalie categories for a goalie, and a word for it: blazing, hot, steady, cold or frozen. Ice time and power-play time per game sit beside the categories for skaters because rising usage is the signal that leads production, and the research behind this page names it as the waiver-wire tell managers look for first, but they are never added into the heat, since a league does not score minutes. Click any column header to sort by that column’s z, click it again to reverse, and the list turns from the hottest in that category to the coldest. A player needs a minimum number of games inside the window to appear, three in the seven-day window, five in fourteen and ten in thirty, so that one big night does not top the list.

Goalies

The goalie tab uses the same maths on save percentage, goals-against average, wins, shutouts, saves and goals against, where the window’s save percentage and goals-against average are ratios of the window’s totals rather than averages of nightly figures, which is how those two statistics are meant to be read. Only games in which the goalie played at least a period count, so a relief appearance after a pulled starter is not a game. A hot goalie is worth checking against the tandem guide before you add him: a backup on a four-game heater who is still the backup starts twice a fortnight.

Comparing two players

The two seats above the list take any two players from the directory, with the arrow keys and Enter working the same way as every search on this site, and lay their three windows side by side: games, each category’s rate and z, and the heat, with the season rate each is measured against. It is built for the moment a trade offer arrives or two free agents are left on the wire and the question is which of them is actually on the rise. The two players do not have to share a position, though a skater and a goalie share no categories and the card says so.

What a trend cannot tell you

A z measures how unusual a stretch is, not why it happened. A winger running hot because he was moved onto the first power-play unit is a different bet from one running hot because four bounces went in, and the page cannot tell them apart; the line sheets and the power-play time column can. A short window is noisy by construction, which is why the minimum games exist and why the fourteen-day window is the default rather than the seven. Before the season opens every window is the end of last season, rosters have changed since, and a player who moved clubs over the summer is measured against a rate he set somewhere else. The window, the categories, the position, the sort and the two compared players are all written into the address, so the link you copy opens the same list for anyone.

The windows are rebuilt from our own game logs every night after the last game is final. If the feed is unavailable the page says so rather than showing a stale list.