Prevent columns from having same value in record
This is called a "many-to-many" relationship. One person can be a member of multiple teams and a team has multiple members. One way to model this, could be:

create table person
(
   person_id integer primary key, 
   name text not null
);

create table team
(
  team_id integer primary key, 
  name text not null
);

create table team_member
(
  team_id integer not null references team, 
  person_id integer not null references person,
  person_role text not null check (team_role in ('lead', 'member')), 

   -- each person can only be assigned to a team once
  primary key (team_id, person_id)
);