The speaker begins by setting up the context for his poem. The poem is a description of a memory recounted from the first-person point of view, as the pronoun "I" in line 3 indicates. This description is addressed directly to someone, the "you" in line 3, who is also the subject of the memory. The apostrophe—the first-person address directly to another person—gives the poem a particularly strong sense of emotional intimacy, almost as if readers are overhearing a private conversation (the speaker's conversation with another person or even with himself, since the "you" being addressed is someone who is not necessarily present to the speaker).
The reader can infer that this memory has strong emotional significance for the speaker. The speaker remembers the exact day when the event took place ("almost to the day") even though it was "eighteen years ago." He delays saying exactly what the event was until lines 3-4, establishing the setting first. The time was a "sunny day with the leaves just turning"—the ending of summer and the beginning of fall, with the leaves just starting to change color. The place was a playing field with "touch-lines," or sidelines, "new-ruled" for the start of the new season. These details not only allow the reader to picture the event but also carry symbolic significance: it turns out that this event marks the end of one season and the beginning of another in the life of the speaker's son, the "you" being addressed.
The event is the son's "first game of football." Participation in organized sports is a traditional rite of passage for young people, especially young men. The football game is a well established, well organized experience. There are touch-lines that demarcate the field and tell the son where he can and can't go, and those lines are "new-ruled," or set down on the field again, at the start of every new season, as the games take place regularly every year. But even if football is a familiar tradition in the larger culture, it is new for this particular boy. He has to learn the rules and rituals that belong to this unfamiliar environment.
The first stanza also establishes the irregular meter of the poem. The irregular meter, combined with the frequent device of enjambment, means the poem sounds less like a formal artistic artifact and more like the authentic, spontaneous recollection of a genuine memory.