Lyric discussion by LAS 

My interpretation of the song is that it's about confronting the inevitability of dying. Remember, the singer is a grandfather--his son, Sonny, has at least one child. While I can't interpret every line, there are several that could refer to the problems of aging:

"Or maybe I'm a dog who's lost its bite": losing one's teeth, or perhaps (more abstract), becoming ineffectual

"I don't expect to sleep through the night": due to urinary frequency from prostate problems

"I don't expect to be treated like a fool no more": asking not to be patronized because of his age

"some rooms are like cages": Sonny could be thinking about another problem of aging, possibly affecting his father: an illness like a stroke or perhaps a broken hip, limiting his mobility and making him bedridden or otherwise confined to his room (which thus becomes a cage)

The lines about Sonny leafing through his yearbook, with some of his classmates having already died, could indicate that Sonny, who is also getting older (thinning hair), is nostalgically or wistfully looking back at his life, remembering how it was...maybe even thinking about his own mortality.

All of this is leading up to my interpretation of "the cross is in the ballpark." It means that death--symbolized by the cross, a common grave marker--is coming soon. In this context, "Why deny the obvious, child?" [punctuation added by me] could be telling Sonny to face up to it: his father is going to die soon (and so will Sonny, eventually).

Given the above, it is rather uplifting that the song is not a dirge; the arrangement is in fact very upbeat. Maybe the Dad (the singer) has made his peace with the inevitable and no longer fears it.

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