I heard an announcer the other day chide a struggling team by saying, "They're not playing that good baseball right now." This doesn't sound grammatical, but my ears have deceived me before. Of course you could say instead, "They haven't been playing well of late," but I want to know if the first statement is grammatical as is.
It is from the idiom The baseball is not (all) that good, The house is not (all) that big, The monkey is not (all) that clever.
It is a valid idiom where the all that substitutes as a less emphatic form of very or much.
From this we derive They are not playing (all) that good, The new house is not (all) that bigger than the old one. She is not (all) that taller than her sister.
As usual there are two kinds of 'grammatical'. There is the more formal school book grammatical, used by school teachers and newspaper editors and news announcers. Then there is how people speak informally.
'That good baseball' is either wrong or infelicitous in formal speech. It could only mean 'The good kind of baseball playing that I am referring to there'. But in context that is surely not what the baseball announcer intends.
In a less formal context, like baseball announcing, 'that' is an adverb like 'very' or 'such a', modifying 'good'. It means 'good to that extent'. This sounds infelicitous even in the informal setting because you really feel like saying 'that good a game', but 'baseball', referring to the general metaphorical idea, is a more abstract thing than a particular game.
The end result is that you probably don't want to use this formation in writing a school paper (eg 'The trade agreement didn't lead to that terrible economic conditions') but is OK informally eg 'Why you cooking that harsh a meth?' (and the syntax of it is rule based to 'that ADJ a NOUN')
Maybe throwing an "of" in there will improve it: "They're not playing that good of baseball right now." Generally "that good" followed by a noun seems to need an "of" like "She's not that good of a secretary." I was also thinking "He didn't do that good of a job," but "He didn't do that good a job" also sounds grammatical to me.
Of course, there is what I think is an unquestionably fine alternative:
They're not playing very good baseball right now.
But the announcer could have intended "that good baseball" as noun itself, i.e. that particular type of baseball, something like:
They're not playing "that good baseball" right now.
They're not playing that "good baseball" right now.