The phrase "a crack for a" is not correct and lacks clarity in written English.
It may be used in a context where you are referring to a specific opportunity or opening, but it needs additional context to be meaningful.
Example: "He found a crack for a chance to showcase his talent during the audition."
Alternatives: "an opportunity for a" or "a chance for a".
On May 5th, a week after the images from Abu Ghraib were first broadcast, the White House opened the window a crack for a dramatic defenestration.
The debate is really over whether to open the door a crack for a new public plan to compete with the private plans.
"Could your sense of smell be a crack for a brain hacker?" While contemplating that, also contemplate this: The coming age of brain hacking could exacerbate an already irksome television trend.
Journalist John Reed attended the trial, and wrote of his impressions of Landis: Small on the huge bench sits a wasted man with untidy white hair, an emaciated face in which two burning eyes are set like jewels, parchment-like skin split by a crack for a mouth; the face of Andrew Jackson three years dead ... Upon this man has devolved the historic role of trying the Social Revolution.
"I do think the window has opened a crack for us to get a political resolution in Syria," Obama said.
By Robin Wright August 6, 2015 "I do think the window has opened a crack for us to get a political resolution in Syria," Obama told a group of journalists.
Cover the pot with a lid, leaving a crack for steam to escape.
Though he dreams of becoming a rap star, Ulysses begins dealing crack for a neighborhood drug lord named Buddha.
Both characters are hugely engaging and I really liked the descriptions, for example, Pullman described the scarecrow's voice as "rich and sonorous" and went on to say "his head was made of a great knobbly turnip, with a broad crack for a mouth and a long thin sprout for a nose…" The book is spiked with humour.
