some indication of regression with respect to his strengths shown last year. PFF's pre-season analysis of ND said this about Book (link below):
Among returning Power Five quarterbacks, Book posted the fourth-best negatively graded play rate and just a 2.0% turnover-worthy play rate (eighth) on throws from a clean pocket. Along with that, Book showed outstanding accuracy when pressure was kept at bay, as he recorded the second-highest “accurate plus” rate and third-lowest uncatchable pass rate, per PFF’s quarterback charting system.
However, when the pass-rush did get home, Book’s play declined significantly as he ranked in the bottom fourth in PFF grade against pressure. Though most of this pressure wasn’t let up by the offensive line, it was because Book brought it on himself.
As a first-year starter, Book bailed on the pocket far too often and had the most pressures allocated to himself among all college football quarterbacks (29 total). Out of those 29 pressures, 18 ended as a sack which was seven more than any other college quarterback. This type of instinct is as expected from a first-year college starter, and it has been proven that performance under pressure is unstable from year to year, so as a result, if Book trusts the pocket and his offensive line, good things will come.
Last night Book threw a number of inaccurate passes from the pocket and showed no improvement, if not regression, under pressure. Given that Golson, Kiser and Wimbush all regressed in their 2nd year as starters before him, there's reason to be concerned.
Link: "Led by Ian Book and an underrated defense, Notre Dame is set to dethrone the Power Five in 2019"