Noticeable in the first stanza of Stanley Kunitz’s poem, “King of the River,” is its minimal enjambment: Most lines are end-stopped. As Edward Hirsch wrote in A Poet’s Glossary, an end-stopped line is “A poetic line in which a natural grammatical pause, such as the end of a phrase, clause, or sentence, coincides with the end of a line . . . It imparts a feeling of completeness (203). (Lines that are not end-stopped, that run on, are enjambed.)
Brewer, on writersdigest.com, defines an end-stopped line as one in which “your line finishes its thought (often with the use of punctuation) before moving on to the next line.” Thus, punctuation can be used, but is not essential, to indicate that a line is end-stopped.
In “King of the River,” the first 8 lines all are end-stopped with a comma.
Line 9 contains just one word, the present participle “tumbling,” without any punctuation. Grammatically, it’s the start of the participial phrase “tumbling over the rocks,” the last three words the contents of line 10. Does “tumbling” effect a “natural grammatical pause.” If it were used this way, it would: “Tumbling, the child scraped his knee.” But in line 9, if Kunitz had placed a comma at line’s end, it would have been misplaced, i.e., “tumbling, / over the rocks” inserts an unwanted pause.
Line 11, “till you paint them,” however, though unpunctuated, is end-stopped because it is a subordinate clause with “till” (until) the subordinating conjunction.
The stanzas last four lines are all end-stopped, ending with these markers: a colon, two commas, and a period.
Further, one line (8) has punctuation within it in addition to a final period: “slapping, thrashing.” That internal punctuation creates a pause within the line called a caesura.