Striking Pleadings - Generally. Potis Holdings Ltd. v. The Law Society of Upper Canada
In Potis Holdings Ltd. v. The Law Society of Upper Canada (Ont CA, 2019) the Court of Appeal stated a basic principle of R21 determinations:
 The essential principles governing a motion to strike out a pleading under r. 21.01(1)(b) as disclosing no reasonable cause of action are well known. A pleading will be struck out if, assuming the facts pleaded to be true, it is plain and obvious that it discloses no reasonable cause action; that is, where it has no reasonable prospect of success: R. v. Imperial Tobacco, 2011 SCC 42,  3 S.C.R. 45, at para. 17; Hunt v. Carey Canada Inc., 1990 CanLII 90 (SCC),  2 S.C.R. 959, at p. 980; and McCreight v. Canada (Attorney General), 2013 ONCA 483, 116 O.R. (3d) 429, at para. 39.. Asghar v. Toronto Police Services Board
In Asghar v. Toronto Police Services Board (Ont CA, 2019) the Court of Appeal sets out some principles of R21 motions to strike pleadings:
The governing principles. Das v. George Weston Limited
 In a motion to strike a pleading as disclosing no reasonable cause of action under r. 21.01(1)(b), the moving party must show that it is “plain, obvious and beyond doubt that the claim will not succeed” at trial: MacKinnon v. Ontario Municipal Employees Retirement Board, 2007 ONCA 874, 88 O.R. (3d) 269, at para. 19. The court added, at para. 20, that “[t]he statement of claim must be read generously to allow for drafting deficiencies” and “[i]f the claim has some chance of success, it must be permitted to proceed.” The court concluded, at para. 21, that “the threshold for sustaining a pleading on a Rule 21 motion is not high.” See also Doe v. Metropolitan Toronto (Municipality) Commissioners of Police (1990), 1990 CanLII 6611 (ON SC), 74 O.R. (2d) 225 (Div. Ct.), leave to appeal refused, 1991 CanLII 7565 (ON CA),  O.J. No. 3673 (C.A.).
In Das v. George Weston Limited (Ont CA, 2018), an international tort case, the Court of Appeal discusses the criteria for deciding R21 motions to strike claims as showing no reasonable cause of action:
 I do not accept these submissions. The proper approach to a r. 21 motion to strike a claim as disclosing no reasonable cause of action is easy to state: the motion judge is to accept the facts pleaded in the statement of claim as true to determine whether it is plain and obvious based on the current state of the law, including how it may be open to development, that the claim discloses no reasonable cause of action.. Koohestani v. Mahmood
 That said, while the material facts that are pleaded in the statement of claim are assumed to be true for purposes of a motion to strike, bald conclusory statements of fact and allegations of legal conclusions unsupported by material facts are not: see Castrillo v. Workplace Safety and Insurance Board, 2017 ONCA 121 (CanLII), 136 O.R. (3d) 654, at para. 15; Apotex Inc. v. Eli Lilly and Company, 2015 ONCA 305 (CanLII), 334 O.A.C. 99, at para. 21, leave to appeal refused,  S.C.C.A. No. 291; Gratton-Masuy Environmental Technologies v. Ontario, 2010 ONCA 501 (CanLII), 101 O.R. (3d) 321, at paras. 101-3. Furthermore, the motion judge is entitled to examine documents that form part of the pleading as part of the material facts that are pleaded and accepted for the purpose of the motion: Web Offset Publications Ltd. v. Vickery (1999), 1999 CanLII 4462 (ON CA), 43 O.R. (3d) 802 (C.A.), at p. 803.
 In R. v. Imperial Tobacco, 2011 SCC 42 (CanLII),  3 S.C.R. 45, at para. 19, McLachlin C.J. explained that the power to strike out a claim is “a valuable housekeeping measure” that allows the court to weed out claims at an early stage while ensuring that claims “that have some chance of success go on to trial.” While the appellants submitted that any claim should be allowed to proceed unless it has been specifically addressed and rejected as legally untenable by the courts, relying on Dalex Co. v. Schwartz Levitsky Feldman (1994), 1994 CanLII 7290 (ON SC), 19 O.R. (3d) 463 (Gen. Div.), at p. 466, the Supreme Court’s articulation in Imperial Tobacco is the binding test. In that case, the court confirmed that a claim will not be struck simply because it is novel: at para. 21. If, however, it is plain and obvious that the pleading discloses no reasonable cause of action, it cannot proceed: Imperial Tobacco, at para. 17; see also Hunt v. Carey Canada Inc., 1990 CanLII 90 (SCC),  2 S.C.R. 959, at p. 980. It must have a “reasonable prospect of success”: Imperial Tobacco, at para. 17.
In Koohestani v. Mahmood (Ont CA, 2015) the Court of Appeal made the following useful comments on principles to be applied by the court when striking a party's defence:
 Notwithstanding the legitimate concerns raised before Spence J., my difficulty with his decision to strike the appellants’ defence is that he failed to apply the principles relevant to such a request, particularly those set out by this court in Bell ExpressVu Limited Partnership v. Corkery, 2009 ONCA 85 (CanLII), 94 O.R. (3d) 614. In Bell ExpressVu, at para. 35, the majority identified striking out a defence as a severe remedy and made it clear that it should generally not be imposed as a remedy of first resort. The defaulting party should, at least, be provided with an opportunity to cure the default.
 Such was not done in this case.
 This failure is of particular note given the order of Roberts J. was not finally settled until November 6, 2013, the day before the motion to strike. The record suggests to me that it was the appellants’ recusal motion and on-going attempts to re-argue the merits that led to such profound delay in settling the terms of the order. Nonetheless, the November 6, 2013, endorsement indicates that on that day a non-trivial change was made to the December 12, 2012 order – namely the removal of any reference to declaratory relief. The respondent has not disputed that the time for appealing the order continued to run when the parties appeared before Spence J. Given the on-going willingness of Roberts J. to hear further submissions and alter the order into November 2013, and the extant right to appeal that order when the motion was argued before Spence J., it is possible that the appellants did not fully appreciate the peril of not paying the damages and costs ordered by Roberts J.
 In addition to the primary principle identified in Bell ExpressVu, - that striking out a defence should not be the remedy of first resort, additional factors should be taken into account in deciding whether to strike a defence for failure to comply with court orders.
 First, the action should be examined with particular attention to the merits of the defence: Bell ExpressVu, at para 36. The pleading and any evidence relevant to the defence may demonstrate a strong defence supporting the conclusion that the interests of justice warranted finding another way to sanction the misconduct. On the other hand, a blatantly unmeritorious defence may give rise to the inference that the defendant’s refusal to comply with a court order is part of a deliberate strategy to delay a decision on the merits – conduct that may justify the imposition of a more severe sanction.
 In my view, it cannot be said that the appellants’ defence in this case is obviously without merit.
 Second, the context of the misconduct relied upon is relevant to the determination of a response that is not only proportional to the severity of the misconduct but also in keeping with the overarching objectives that guide the application of the rules; namely, that set out in r. 1.04 that the rules should be interpreted to secure the just determination of each civil proceeding on its merits.
 In this case, the misconduct that led to the striking of the defence took place in the context of a peripheral dispute involving a relatively small amount (just over $15,000) in relation to the amount in issue, at least as pleaded (over $680,000). See Tarion Warranty Corp. v. 1486448 Ontario Inc., 2012 ONCA 288 (CanLII), 2012 CarswellOnt 5355.
 Third, in some cases the record may indicate that it was counsel for the defaulting parties rather than the parties themselves who should bear primary responsibility for the misconduct in issue. As stated by Sharpe J.A., writing for the court in Marché D’Alimentation Denis Thériault Ltée v. Giant Tiger Stores, 2007 ONCA 695 (CanLII), 87 O.R. (3d) 660, at para. 28, “The law will not ordinarily allow an innocent client to suffer the irrevocable loss of the right to proceed by reason of the inadvertence of his or her solicitor”.