Before it has a chance to go two blocks"

Rhythm and Meter: Updike's poem is written in a fixed form, iambic pentameter, which means each line contains five (5) iambs. 

Rhythm: an iamb is an unstressed syllable followed by a stressed syllable, like the word "beFORE." 

Meter: The repetition of five poetic feet (an iamb is one example of a poetic foot) in a line is termed "PENTAMETER," a combination of the Greek word for five, PENTA and the word METER.

Here is line three re-written to show the rhythm/meter:

"beFORE it HAS a CHANCE to GO two BLOCKS" 

Each line in the poem is written in IAMBIC PENTAMETER. NOTE: not all lines will be perfect examples of five iambs; the key is to look for a poem's overall pattern.

Flick is a gas station attendant at Berth's Garage now, tending the gas pumps, "five at a side.” Edward Hopper depicts the "old bubble-head style" pumps in the painting above.

In a way, the pumps have a human figure: a distinct head, a long, upright body, with hoses that could be loose gangly arms.

One might even say they resemble a basketball player with tall, long arms.

Alliteration: Did you notice the repetition of consonant sounds in this line?

Grease and gray, kind and coiled, and plays and pinball.

Situational irony: with the audiences of high school gyms now gone, Flick "nods...toward bright applauding tiers/Of Necco Wafers, Nibs, and Juju Beads."
Given the fame and PROWESS (extraordinary ability) of Flick's high school days, one might say his current state is quite unexpected.