gg5 usage note: 英語の "dead ball" は「競技中 (in play) でないボール」の意.

As a matter of policy, we don't tag things "wasei" if they're not Japanese constructions, no matter how much the meaning might differ from the original English expression.

@@ -13 +13 @@
-<lsource ls_wasei="y">dead ball</lsource>
+<lsource xml:lang="eng">dead ball</lsource>

It can stay as in  Stephen's note, or the wasei tag could go and "dead ball" be added as a second gloss. I have seen other cases of rather stretched wasei tagging by kokugos.

Daijr/s, koj, shinmeikai, oukoku, and meikyo all label this word as 和製, and most of them note that its Japanese usage corresponds to the phrase "hit by a pitch" in English. Nikkoku also contains this note, but does not label the word as 和製. Iwakoku does not label it 和製, but rather 日本独特の用法.

I think the 和製 claim is questionable. Its meaning in Japanese merely seems to be restricted to a narrow subset of its meanings in English. When a player is hit by a pitch, a Japanese announcer would likely describe the situation as a デッドボール, while an American announcer would probably say "hit by pitch." But if you were to ask the American announcer whether the ball that hit the player is dead or not, they would absolutely agree that it is. (Wikipedia lists hit-by-pitch as its first example of a dead ball: https://en.wikipedia.org/wiki/Dead_ball#Baseball)

Nikkoku gives an example of 死球 in this sense from 1896, and an example of デッド‐ボール from 1934. Google's "Books Ngram Viewer" shows that "dead ball" became common in written English starting in the 1860s. Japanese Wikipedia says baseball was only introduced to Japan in 1871 (https://ja.wikipedia.org/wiki/野球の歴史#日本における野球の歴史).

I don't know if I'm in any position to question six major kokugo dictionaries, but I thought I'd at least leave a note. To me it seems like they think it's 和製 simply because its situational usage in Japanese differs slightly from English. If that's sufficient, I'd think just about every loanword would be 和製.

gg5

@@ -14 +14 @@
-<gloss>hit a batter by pitching a ball</gloss>
+<gloss>pitch that hits the batter</gloss>