Sign stealing in baseball

Question

I don't understand the current sign stealing issue between the Red Sox and the Yankees. I don't understand how sign stealing in baseball actually works. Just seeing a catcher's sign is not enough.

How can a team know what their opponents' signs actually mean?

Doesn't each team have their own signs?

Don't they change their meanings now and then like a password?

Edit:

The Boston Globe quotes Red Sox second baseman Dustin Pedroia:

Our adjustment to that stuff is: go out to the mound and change the signs.

OK, I guess one could identify the current signs at the start of a game by watching the signs and the pitches that follow. Yahoo describes this process:

if someone on a team’s video staff cracks an opponent’s signals, they are run from the video room to an intermediary in the dugout and forwarded to players on the field

But that process would take longer than the actual at bat itself and the information would never reach the batter in time. The only benefactor would be the runner at second base who will know when to steal a base. But he should be able to see the catcher's signs directly and wouldn't need a relay chain.

Of course, that runner could alert the batter directly on what pitch to expect once the signs have been cracked. The Boston Globe describes this:

Often times it happens when a runner at second base peers in to see the catcher’s sign and then subtly flashes a signal — maybe a hand movement, or the positioning of his feet — to the batter to let him know whether the next pitch will be a fastball, curveball or something else.

But how often is there a runner at second base during a game? It's not that big of an advantage in my opinion. And I'm pretty sure all teams have been doing this for 150 years or so.

Disclaimer: I have never played baseball myself, unfortunately. I'm just an interested spectator so please bear with me.

Answer 1

Sign stealing is pretty easy - you watch the signs and then match the corresponding pitches. The signs indicate what kind of pitch (fastball, change-up, slider, curve, etc.) and often the placement - down the middle, inside. low/high, etc. If you know that a batter has a hittable pitch and can relay that to them before the ball comes it greatly improves their chances at getting a hit and avoiding pitches that are likely to result in a swing and a miss.

Certainly a runner at 2nd base would have the best view of the catcher to see what signs issued, but the team at bat also has coaches at first and third bases who both have a pretty good view of the catcher.

But the real way this is being done today is through the use of the live television feed which teams use for instant replay on their jumbotron screens throughout the park. Tom Verducci writing here for Sports Illustrated, says that use of the live feed became an issue when Major League Baseball instituted instant replay to review some calls in 2009.

It is common practice in baseball to steal signs and not technically against the rules. One reason you see players come out to surround a pitcher is that the team changes signs during a game. Where the Red Sox broke an actual rule, and not just ethics, was in the use of electronic equipment in the dugout. The only communication device in a baseball dugout that uses electricity is supposed to be the analog phone that is connected to the bullpen. Unlike most sports that have headsets, tablets, etc. baseball opts for the tradition of the past and says you cannot use any electronic communications in the dugout - so no one even has a cell phone. They do allow tablets, but they cannot receive information during the game - all data is preloaded (batter spray charts, pitcher tendencies, etc.)

The Red Sox had someone who watched the video monitor in real time to get the sign and sent sign to a coach with an Apple Watch who could whistle to indicate either a pitch that they could hit or to avoid.

An old adage in baseball is, "If you ain't cheatin' you ain't tryin'." Sign stealing, baseball hiding, ball altering are accepted common practices, but if you are found with a nail file or use electronic means, etc. and get caught you are penalized.