Many of us are aware of how much stock baseball announcers, commentators, fans, managers, coaches, and players put in the significance of a player or team being hot or cold. It is nearly impossible to watch or listen to a game without the commentator at some point remarking that, “So-and-so has been red-hot or ice-cold,” referring to the fact that said player has recently had a very good or very bad spate of performance.

While there is no doubt that players and teams go through short, and even long, periods of time when their performance is well above or below their norm, the question that this chapter examines is, “Is there any predictive value to these hot and cold streaks?” Another way to couch this question is, “Are hot and cold streaks solely a result of normal, random fluctuation, or are they due to a combination of random fluctuation and a temporary change in a player's ability?”

It is unlikely that fans, commentators, baseball pundits, and the like, are infatuated with hot and cold streaks simply for the sake of pointing out what has already happened. To mention that, “So-and-so has hit over .400 in his last five or ten games,” with no implication that this has anything to do with how we expect him to hit in the near future would be banal. The fact is that when most people talk about hot and cold streaks, they generally believe that these streaks do, in fact, have predictive value—that a player (or team) who has been hot is expected to hit better than his norm in the near future, and that a player who has been cold will continue to be cold, at least for some finite period of time. This belief is evidenced by several things that occur in baseball:

• Managers will sometimes bench regular players who have been cold, or start reserve or part-time players who have recently been hot.
• Managers will often rearrange their batting orders depending upon who is hot and who is cold.
• Opposing managers will occasionally pitch around or even intentionally walk hot players and pitch “right at” cold players.
• Managers will sometimes play small ball when their offenses have been cold, and eschew such an approach when their hitting has been hot. How often have we heard an announcer say, “So-and-so (team) is sacrificing in the first or second inning because they have had trouble scoring runs lately?” The clear implication is that because the team has been cold (hitting-wise) in the past few games or weeks, they are likely to score fewer runs than normal in the current game.
• Finally, fans and sports handicappers regularly assess the current strength of a team depending, at least in part, upon whether its players, as a whole, have been hot or cold in the recent past.

This chapter looks at what happens exactly one game immediately following a five-game hot or cold streak, as well as what happens over a five-game period immediately following that same hot or cold streak. If the fans, commentators, and pundits are right, players, as a group, should hit significantly better than their own normal level of performance for some period of time following a hot streak, and significantly worse following a cold streak. While it might be difficult to predict how long this effect would last, either our one-game or our five-game snapshot (or both) should capture this effect, if in fact it does exist.

At this point you might be thinking, you are looking at a one or five-game period after a streak has been identified, therefore the streak may be over. Remember, however, that in real life we are always looking at a point in time subsequent to a streak—the streak is always in the past. While we may have no idea whether the streak is over or not, our (actually, their) hypothesis is that there is still something left to the streak, at least for some period of time in the near future. Let's see if this is true, and if so, to what extent.