The Collaborative International Dictionary of English v.0.48:

Catching \Catch"ing\, n.
   The act of seizing or taking hold of.
   [1913 Webster]

   Catching bargain (Law), a bargain made with an heir
      expectant for the purchase of his expectancy at an
      inadequate price. --Bouvier.
      [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

CATCHING BARGAIN, contracts, fraud. An agreement made with an heir
expectant, for the purchase of his expectancy, at an inadequate price.
     2. In such case, the heir is, in general, entitled to relief in equity,
and way have the contract rescinded upon terms of redemption. 1 Vern. 167; 2
Cox, 80; 2 Cli. Ca. 136; 2 Vern., 121; 2 Freem. 111; 2 Vent. 329; 2 Rep. in
Ch. 396; 1 P.Wms. 312; 3 P.Wms. 290, 293, n.; 1 Cro. C. C. 7; 2 Atk. 133; 2
Swanst. 147, and the cases cited in the note; 1 Fonb.140 1 Supp. to Ves. Jr.
66 Id. 361 1 Vern. 320, n. It has been said that all persons dealing for a
reversionary interest are subject to this rule, but it may be doubted
whether the course of decisions authorizes so extensive a conclusion and
whether, in order to constitute a title to relief, the reversioner must not
combine the character of heir. 2 Swanst. 148, n. Vide 1 Ch. Pr. 112, 113,
n., 458, 826, 838, 839. A mere hard bargain is not sufficient ground for
relief.
     3. The French law is in unison with these principles. An agreement,
which has for its object the succession of a man yet alive, is generally
void.Merl. Rep. mots Succession Future. Vide also Dig. 14,6, and Lesion.