Learn Hardcore Indonesian: Di siaran langsung itu, hasil pertandingan hanya kelihatan sekilas lalu strategi dibahas panjang. - In that live broadcast, the match result is only seen briefly, then the strategy is discussed at length.

di here means “on/at,” like “on that live broadcast.” It’s the most natural preposition for media surfaces: di TV, di radio, di siaran.
itu points to a specific, known broadcast: “that (particular) live broadcast.” In Indonesian, itu often works like a definite article (“the”) when the thing is identifiable.
pada is a bit more formal and works too: pada siaran langsung itu.
dalam (“in/within”) focuses on being “inside” something; with broadcasts it can sound bookish or spatially literal. You’ll hear it, but di is the default.

Is the comma after the opening phrase necessary?

It’s optional but helpful. Commas commonly set off a fronted time/place/topic phrase in Indonesian. So: Di siaran langsung itu, … is clear and standard, but leaving the comma out wouldn’t be wrong.

Who’s doing the discussing in “strategi dibahas panjang”? There’s no subject.

Indonesian often uses the passive with no agent.

strategi = patient/thing discussed
dibahas = “is discussed” (passive: di- + bahas)
Agent is understood (hosts, commentators). You can add it if needed: strategi dibahas (oleh para komentator) panjang (lebar).

What’s the difference between kelihatan, terlihat, tampak/nampak, and keliatan?

kelihatan: everyday/neutral; can mean “is visible” or “looks/seems.”
terlihat: neutral-to-formal; often preferred in writing.
tampak/nampak: more formal/literary; nampak is also regional.
keliatan: colloquial spelling/pronunciation of kelihatan.
In this sentence, kelihatan = “was visible.”

Does kelihatan mean “visible” or “seems”? Which reading applies here?

Here it’s “visible.” The phrase kelihatan sekilas (“visible only briefly/at a glance”) forces the “can be seen” reading, not the “seems/appears” reading you might get with adjectives (e.g., kelihatan capek = “looks tired”).

How do sekilas, sekilas lalu, sepintas (lalu), and sebentar differ?

sekilas: “at a glance/briefly (by sight).”
sekilas lalu: “in passing/only at a glance” (colloquial-ish; emphasizes fleetingness).
sepintas (lalu): very close to sekilas (lalu); common in writing.
sebentar: “for a short time” (time-focused, not specifically about a glance).
All can suggest brevity, but sekilas/sepintas (lalu) highlight a fleeting look, not just a short duration.

Is “sekilas lalu” a set phrase here, or is lalu the connector “then”?

It can be parsed either way in theory:

sekilas lalu can mean “in passing.”
lalu can also be the clause connector “then.”
Context suggests the connector: “visible briefly, then the strategy was discussed…”. A comma helps: … kelihatan sekilas, lalu strategi …. If you want the fixed phrase, you can say kelihatan sepintas lalu to avoid ambiguity.

What exactly does hanya limit here, and is its position important?

In hasil pertandingan hanya kelihatan sekilas, hanya limits the predicate: “was only briefly visible.”
If you want to limit the subject instead (Only the match results, not other things), use a yang-construction: Hanya hasil pertandingan yang kelihatan sekilas. Word order changes the focus.

Is “Hasil pertandingan hanya sekilas kelihatan” okay?

Yes, it’s understandable but less common. The more typical flow is hanya kelihatan sekilas. If you front hanya to modify the subject, prefer adding yang: Hanya hasil pertandingan yang kelihatan sekilas.

What’s going on with “dibahas panjang”? Isn’t panjang an adjective?

Correct—panjang is an adjective (“long”). Indonesian often lets adjectives function adverbially after verbs.

dibahas panjang = “discussed at length.”
It’s a clipped form of the idiom panjang lebar (“at great length/in depth”): dibahas panjang lebar.

Is “dibahas dengan panjang lebar” correct? What about “secara panjang lebar” or “mendalam”?

dibahas panjang lebar: most idiomatic and common.
dibahas dengan panjang lebar: also good.
dibahas secara panjang lebar: heard, but less natural than the two above.
Alternatives: dibahas secara mendalam, dibahas tuntas, dibahas secara rinci—all mean “in depth.”

How would I say the second clause in active voice naturally?

Use an agent subject:

Lalu para komentator membahas strategi panjang lebar.
Lalu mereka membahas strategi secara mendalam.
Avoid membahas strategi panjang (it can read as “a long strategy,” not “discuss at length”).

Can lalu be replaced with kemudian or terus? Any nuance?

lalu: neutral connector (“then/and then”).
kemudian: a bit more formal/sequencing (“after that/then”).
terus: very colloquial/conversational (“and then/so then”).
All work here; pick by register.

Should it be “hasil pertandingannya” or “hasil pertandingan itu” if I mean a specific match?

Both specify definiteness:

hasil pertandingannya = “its/the match’s results” (the -nya makes it definite/possessive).
hasil pertandingan itu = “the results of that match.”
Without -nya/itu, it can be read as general or contextually definite.

Is “di siaran langsung itu” the only natural way? Could I say “pada acara itu,” “di tayangan langsung itu,” or “di TV”?

All are possible, with nuance:

di siaran langsung itu: “on that live broadcast.”
di tayangan langsung itu: similar; tayangan emphasizes the telecast/program.
pada acara itu: “on that program/show” (more formal).
di TV/di televisi: broader medium reference.
Choose based on how specific you want to be and your register.