A dictionary of Confusable Phrases: More Than 10,000 Idioms and Collocations

Note: 
The expression does not correlate in meaning with the
phrase pull off a hat-trick—(usually of sports) have three suc-
cesses in a row: This thoroughbred is ridden by Peslier, who
has already pulled off a hat-trick of three consecutive Prix de
l’Arc de Triomphe successes.
See also: have something under one’s hat / keep something under
one’s hat.
pick up on someone • pick up with someone
pick up on someone —
1
. (Racing ) draw near a person; begin
to overtake a competitor: Benedict, knowing that he had the
fastest car, was inclined to allow Chalmers to pick up on
him…. 2. (U.S. coll.) understand or appreciate a person: After
Baudelaire picked up on him, Edgar Allen Poe had enormous
influence on French literature and art.
pick up with someone —enter into conversation and make
acquaintance with smb. casually met: So you’ve let your Polly
go and pick up with some young man from town.
Note: 
Neither expression correlates in meaning with the phrase
pick someone up—
1
. take a person along with one, into one’s
company or into a vehicle (collecting him from a place): I remem-
ber picking him up from work that night to take him home
(he had no car). 2. form an acquaintance with a person casually
or informally, especially with the intention of having a sexual
relationship: She wished she had not picked Markie up in the
train and given him her address. 3. (coll.) find fault with a per-
son; call smb. to account: I am picked up for saying that the
initiative in the Steamer case should have come from the stew-
ards. 4. (sl.) rob, cheat, or swindle a person: There are loose
characters lurking about, on the look-out for strangers, to
“pick them up,” as they term it, which, in other words, means
to rob them. 5. cause a person to revitalize; serve as a “pick-me-
up”: Have you had your tea? A cup of tea will pick you up. 6.
(sl.) arrest or apprehend a person: Things start to go badly for
him. His boys … get picked up for every minor charge in the
book.