Learn Hardcore Spanish (Latin America): Esos tenis nuevos son cómodos, pero no son para correr hoy. - Those new sneakers are comfortable, but they are not for running today.

estos/estas = “these,” near the speaker.
esos/esas = “those,” closer to the listener or at a middle distance.
aquellos/aquellas = “those (over there),” far from both speaker and listener. Here esos suggests the sneakers are not with the speaker, but not very far away either.

Does tenis mean the sport or the shoes?

Both, depending on context:

el tenis = the sport “tennis” (singular, masculine).
los tenis = sneakers/tennis shoes (plural, typically masculine in much of Latin America). The plural article and the rest of the sentence (comfort, running) clearly indicate shoes here.

Is tenis singular or plural? What gender is it?

For “sneakers,” tenis is usually treated as masculine plural: los tenis, unos tenis, esos tenis.
To refer to one sneaker, people often say un tenis (very common in Mexico) or just un zapato/una zapatilla. A safe neutral option is un par de tenis for “a pair of sneakers.”
In some regions you may hear feminine plural (las tenis), but los tenis is more widespread.

Why is the verb son plural?

Because the subject tenis is plural. Spanish verbs agree in number with their subject: los tenis … son.

Why cómodos (with accent) and not comodos or cómodo?

Agreement: tenis is plural masculine, so the adjective must be cómodos (not singular cómodo).
Accent: Without an accent, the default stress would fall on the second-to-last syllable (co-MO-dos). The correct stress is on the first syllable (CÓ-mo-dos), so Spanish marks it with an accent: cómodos.

Why pero and not sino?

pero = “but,” adds a contrast: “They’re comfortable, but they’re not for running today.”
sino = “but rather,” corrects a previous negative: No son para correr, sino para caminar (“They’re not for running, but rather for walking”). Here the first clause isn’t negated, so pero is the right choice.

Why para and not por in para correr?

para + infinitive expresses purpose or suitability: son para correr = “they’re for running.”
por + infinitive expresses cause/reason: Te castigaron por correr = “They punished you for running.” Since we’re talking about intended use, para is correct.

Can I say tenis de correr instead of tenis para correr?

Yes. Both are used:

de + noun/infinitive often labels a type: tenis de correr, zapatillas de correr, ropa de dormir.
para + infinitive highlights purpose: tenis para correr. In many places you’ll hear both; de correr can feel a bit more “label-like.”

Should it be son or están in this sentence?

ser for inherent/classifying traits of things: Los tenis son cómodos (that’s their quality), No son para correr (they’re not designed for that).
estar for temporary states/conditions: Los tenis están sucios (dirty now), No están para correr hoy (they’re not in condition for running today—e.g., wet, untied, new and not broken in). Your sentence with son suggests a classification/purpose. If you mean “not in suitable condition today,” use no están para correr hoy.

Is putting hoy at the end okay? Where else could it go?

Yes, it’s fine at the end. Other natural placements:

Hoy no son para correr.
No son para correr hoy. Moving hoy earlier puts more emphasis on “today.”

Why is there no article like los before tenis?

Because esos is a demonstrative determiner and already specifies the noun. You normally use either a demonstrative (este/ese/aquel) or a definite article (el/la/los/las), not both. Without the demonstrative, you could say: Los tenis nuevos son cómodos…

Why tenis nuevos instead of nuevos tenis? Is there a meaning difference?

Spanish usually places descriptive adjectives after the noun. With nuevo, position can change nuance:

tenis nuevos = brand-new sneakers (newly made/unused).
nuevos tenis = some new sneakers (new to the owner; another pair), not necessarily “brand-new” as the main point. Both are common; your version focuses on “brand-new.”

Is the comma before pero required?

It’s standard to use a comma before pero when it links two clauses, as here. You’ll almost always see it.

Could I say zapatillas or something else instead of tenis?

Yes, regional terms vary:

Mexico, Colombia, much of Central America: tenis.
Argentina, Chile, Peru and much of the Southern Cone: zapatillas (also zapas informally).
Uruguay: championes (informal).
Venezuela: zapatos deportivos or tenis. All are understood regionally; tenis is a safe pan–Latin American choice.

Any pronunciation tips for words here?

tenis: TE-nis (both vowels pure; one N).
cómodos: stress the first syllable (CÓ-mo-dos).
correr: roll the rr in the middle; stress on the last syllable (co-RRER).
hoy: one syllable, like “oy.”