Благо основание ракетки лёгкое, топ-спин и верхнее вращение легко контролировать.

Here благо is not a noun. It is being used as a conjunction, meaning something like since, seeing that, or it’s a good thing that.

So the structure is roughly:

Благо основание ракетки лёгкое, ...
= Since / luckily the racket base is light, ...

This use of благо is a little stylistically marked compared with very neutral connectors like потому что or так как, but it is perfectly understandable.

Because the sentence is made of two clauses:

1. Благо основание ракетки лёгкое
2. топ-спин и верхнее вращение легко контролировать

The first clause, introduced by благо, gives the reason or favorable circumstance for the second. Russian separates these clauses with a comma.

Because лёгкое agrees with основание.

• основание is neuter
• singular
• nominative

So the adjective must also be neuter singular nominative:

• лёгкий = masculine
• лёгкая = feminine
• лёгкое = neuter

Since основание is neuter, лёгкое is the correct form.

Ракетки is genitive singular.

The phrase основание ракетки literally means the base/blade of the racket. Russian often expresses possession or part-whole relationships with:

noun + genitive

So:

• основание = base / foundation / blade
• ракетки = of the racket

This is very normal Russian structure.

Because Russian normally omits the present-tense form of to be.

So:

• основание ракетки лёгкое literally looks like the racket base light but means
• the racket base is light

This is one of the most basic differences from English.

They are related, but they do different jobs.

• лёгкое is an adjective: it describes a noun
  
  • лёгкое основание = a light base
• легко is an adverb/predicative word: it describes how easy something is
  
  • легко контролировать = easy to control / to control easily

So the sentence uses the same root twice, but in two different grammatical roles.

Because легко + infinitive is a very common Russian pattern for saying that something is easy or hard to do.

So:

• топ-спин легко контролировать means
• topspin is easy to control or literally
• it is easy to control topspin

This is an impersonal construction. Russian often prefers this kind of structure.

If you said легко контролируется, that would mean something more like is easily controlled, which is grammatically possible in some contexts but has a more passive feel and is not exactly the same phrasing.

No. They are best understood as the objects of контролировать.

So the structure is:

• легко контролировать что?
• топ-спин и верхнее вращение

That means they are in the accusative case.

However, they look identical to the nominative here because they are inanimate:

• masculine inanimate singular accusative often looks like nominative
• neuter inanimate singular accusative also looks like nominative

So:

• топ-спин = accusative singular, same form as nominative
• верхнее вращение = accusative singular, same form as nominative

This is why an English speaker might initially mistake them for subjects.

Yes, more or less. It is a borrowed sports term, usually written with a hyphen: топ-спин.

It is generally treated as:

• masculine
• inanimate

In many contexts it can be declined like a normal masculine noun:

• топ-спина
• топ-спину
• топ-спином

In your sentence, though, the form is топ-спин, which matches both nominative and accusative singular for an inanimate masculine noun.

In many sports contexts, yes, they are very close or even effectively equivalent:

• топ-спин = the borrowed international term
• верхнее вращение = a more descriptive Russian term

A writer may use both:

• for emphasis
• for clarity
• to appeal to readers who know one term better than the other

So grammatically, the sentence is simply listing two coordinated things that are easy to control.

Literally it means the base/foundation of the racket, but in sports-equipment language it usually refers to the main body or blade/base part of the racket, not just some abstract foundation.

So this is a normal case where a word’s literal dictionary meaning does not fully match its technical use in context.

Yes. Russian word order is flexible.

This version starts with Благо... to foreground the favorable reason:

• Благо основание ракетки лёгкое, топ-спин и верхнее вращение легко контролировать.

A different order is also possible, for example:

• Топ-спин и верхнее вращение легко контролировать, благо основание ракетки лёгкое.

That would sound a bit different in emphasis, but the grammar still works. Russian often moves material around to highlight what the speaker wants to stress.