The phrase "a weak grasp" is correct and usable in written English.
It can be used to describe a lack of understanding or control over a subject or concept.
Example: "His performance in the exam reflected a weak grasp of the fundamental principles of physics."
Alternatives: "a poor understanding" or "a limited comprehension."
With such a weak grasp of your brief you don't deserve to be a minister.
He had a weak grasp of how political parties worked, and of the role of the American presidency.
Research by Professor Shipps and Freeman of Ohio Wesleyan University found that a weak grasp conveyed "guilt, fatigue and regression".
Government officials recognize that they still have a weak grasp of how much plutonium is contaminating the environment.
Organizations often fail to take into account all of the possible repercussions, and have a weak grasp of how the investments in controls will decrease the probability of a threat.
And if his assessment turned out not to be true, it would make Dimon look like either a dissembler or a manager with a weak grasp of the facts.
Survey findings suggest Orbán has a weaker grasp on what issues truly matter today to central Europeans than the president of the European council, Donald Tusk – a staunch critic of Poland's nationalist government.
In 2005, Mark Levin, a talk-radio host who worked under Meese in the Reagan Justice Department, wrote that Thurgood Marshall, who had challenged originalism, "couldn't have had a weaker grasp of the Constitution".
In fact, says David Evans, an economist at the University of Chicago, he has seen judges in Europe with a weaker grasp of how markets work than those he deals with in Chinese cases.A final cause for concern is that the antitrust campaign confuses and conflates differing, and possibly conflicting, policy goals.
An unpopular president and a House Republican leadership team with a seemingly weak grasp of its own members' priorities is preparing to rush through legislation that would trade 24 million people's health coverage for a huge tax cut on wealthy households and health care corporations.
The presidential debate on Thursday night showed a president with an uncomfortably weak grasp of the impact of his own decisions, and a challenger, John Kerry, who had intelligent, well-planned and achievable solutions to the many problems we face abroad.
